RISC-V Updates for the 4.19 Merge Window

This tag contains some major improvements to the RISC-V port, including
the necessary interrupt controller and timer support to actually make it
to userspace.  Support for three devices has been added:

* Support for the ISA-mandated timers on RISC-V systems.
* Support for the ISA-mandated first-level interrupt controller on
  RISC-V systems, which is handled as part of our core arch code because
  it's very small and tightly tied to the ISA.
* Support for SiFive's platform-level interrupt controller, which talks
  to the actual devices.

In addition to these new devices, there are a handful of cleanups all
over the RISC-V tree:

* Build fixes for various configurations
    * A fix to the vDSO build's makefile so it respects CFLAGS.
    * The addition of __lshrti3, a libgcc derived function necessary for
      some 32-bit configurations.
    * !SMP && PERF_EVENTS
* Cleanups to the arch code to remove the remnants of old versions of
  the drivers that were just properly submitted.
    * Some dead code from the timer driver, most of which wasn't ever
      even compiled.
    * Cleanups of some interrupt #defines, which are now local to the
      interrupt handling code.
* Fixes to ptrace(), which while not being sufficient to fully make GDB
  work are at least sufficient to get simple GDB tasks to work.
* Early printk support via RISC-V's architecturally mandated SBI console
  device.
* A fix to our early debug trap handler to ensure it's always aligned.

These patches have all been through a fairly extensive review process,
but as this enables a whole pile of functionality (ie, userspace) I'm
confident we'll need to submit a few more patches.  The only concrete
issues I know about are the sys_riscv_flush_icache patches, but as I
managed to screw those up on Friday I figured it'd be best to let them
bake another week.

This tag boots a Fedora root filesystem on QEMU's master branch for me,
and before this morning's rebase (from 4.18-rc8 to 4.18) it booted on
the HiFive Unleashed.

Thanks to Christoph Hellwig and the other guys at WD for getting the new
drivers in shape!