GDB port for RISC-V

[Palmer Dabbelt <palmer@dabbelt.com>]

Thanks to everyone who has looked at the RISC-V ports over the last few weeks.
While I think we're not quite done yet, I wanted to get a v2 patch set out so
everyone is on the same page.

Here's the things I think are still left to do

 * File the copyright assignment for todd@bluespec.com.  I've contacted the
   Bluespec people, he's in the middle of submitting the forms.

 * There were a handful of things I didn't understand in a code review.

 * The GDB port doesn't use riscv-opc.h, but I think this is more of a cleanup.

 * We have a patchset for the rest of binutils that changes the ABI around a
   bit, when that lands then GDB will need some updates as well.  I'll either
   incorporate those changes into a v3 or submit them as seperate patches,
   depending on how the sequencing goes.

There are some tiny ChangeLog entries in each patch, I tried to copy what other
new ports did.  Aside from that, I don't know of anything that still needs to
be done.

Thanks for all the feedback!



[PATCH 1/3] RISC-V Sim Port
[PATCH 2/3] RISC-V GDB Port
[PATCH 3/3] Add a RISC-V GDB NEWS entry