With this commit you'll no longer be able to run upstream Rocket Chip
configs by just running

  make CONFIG=SomeRocketChipConfig

instead you'll need to run

  make CONFIG=SomeRocketChipConfig CFG_PROJECT=rocketchip

the advantage is that the boom branch will no longer require any diff
against rocket-chip aside from some default Makefile variables and a
submodule pointer.

Be sure to look at

  https://github.com/ucb-bar/riscv-boom/pull/15

before merging this.

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