Fix issue with PutBlock and Release in BroadcastHub

There is logic in the broadcast hub to skip the outer acquire if there
is an outgoing release, since the data will be written out through the
release channel. However, this will cause an issue in the case of
PutBlock requests. If the tail beats of the PutBlock show up after the
outer release has already been sent, the data will be corrupted.

The fix is to make the outer release block if there are pending
inner PutBlock beats.

Use random, unused port for JTAG VPI

Fixed AsyncFifo with reset messaging

Sometimes we have high performance devices that go inbetween.

When selecting between error generation on R and real data on R,
correctly calculate the R backpressure.

This bug manifests when a valid request is immediately followed by
an invalid request, wedging the R channel.

When there is only one manager, you still want to know if the address
was wrong on the link to that manager!

Sanity check compile-time vs simulation-time options

If user compiles without +define+DEBUG but then requests +vcdfile at
simulation time, that request would be silently ignored. This changes
it to a fatal error.

It's good philosophy to treat plusargs like +vcdfile as commands, not
suggestions, and die immediately if they cannot be honored, instead of
silently ignoring them. Otherwise the user sits through the entire
simulation and then is left scratching his head wondering where his
waveforms are.

Now that we have ifdef VCS in here lets use it for something more than compatibility

More Cadence Incisive fixes

Don't mean to eat up travis bandwidth but shared branches sometimes get made.

This fixes the following compile warnings and simulation errors:

Compile-time warnings:
      $vcdplusfile(vcdplusfile);
                 |
ncelab: *W,MISSYST (/home/scottj/rocket-chip/vsrc/TestDriver.v,42|17): Unrecognized system task or function: $vcdplusfile (did not match built-in or user-defined names) [2.7.4(IEEE Std 1364-2001)].
      $vcdpluson(0);
               |
ncelab: *W,MISSYST (/home/scottj/rocket-chip/vsrc/TestDriver.v,43|15): Unrecognized system task or function: $vcdpluson (did not match built-in or user-defined names) [2.7.4(IEEE Std 1364-2001)].
      $vcdplusmemon(0);
                  |
ncelab: *W,MISSYST (/home/scottj/rocket-chip/vsrc/TestDriver.v,44|18): Unrecognized system task or function: $vcdplusmemon (did not match built-in or user-defined names) [2.7.4(IEEE Std 1364-2001)].
        `VCDPLUSCLOSE
                    |
ncelab: *W,MISSYST (/home/scottj/rocket-chip/vsrc/TestDriver.v,89|20): Unrecognized system task or function: $vcdplusclose (did not match built-in or user-defined names) [2.7.4(IEEE Std 1364-2001)].

Which then become simulation-time errors:

      $vcdplusfile(vcdplusfile);
                 |
ncsim: *E,MSSYSTF (/home/scottj/rocket-chip/vsrc/TestDriver.v,42|17): User Defined system task or function ($vcdplusfile) registered during elaboration and used within the simulation has not been registered during simulation.
      $vcdpluson(0);
               |
ncsim: *E,MSSYSTF (/home/scottj/rocket-chip/vsrc/TestDriver.v,43|15): User Defined system task or function ($vcdpluson) registered during elaboration and used within the simulation has not been registered during simulation.
      $vcdplusmemon(0);
                  |
ncsim: *E,MSSYSTF (/home/scottj/rocket-chip/vsrc/TestDriver.v,44|18): User Defined system task or function ($vcdplusmemon) registered during elaboration and used within the simulation has not been registered during simulation.
        `VCDPLUSCLOSE
                    |
ncsim: *E,MSSYSTF (/home/scottj/rocket-chip/vsrc/TestDriver.v,89|20): User Defined system task or function ($vcdplusclose) registered during elaboration and used within the simulation has not been registered during simulation.
        `VCDPLUSCLOSE
                    |
ncsim: *E,MSSYSTF (/home/scottj/rocket-chip/vsrc/TestDriver.v,97|20): User Defined system task or function ($vcdplusclose) registered during elaboration and used within the simulation has not been registered during simulation.

The SystemVerilog LRM (IEEE 1800-2012) clause 20.15.1 ($random
function) says: "The seed argument shall be an integral variable."

This fixes the following compile warning:

    rand_value = $random($urandom);
                       |
ncelab: *W,WRNOTL (/home/scottj/rocket-chip/vsrc/TestDriver.v,34|23): Argument to out parameter is not a legal lvalue.

Fix Verilog compile warning from Cadence Incisive

AXI4=>TL2 converter