i965: Mad hacks to avoid using MRFs on Ivybridge.

i965: Mad hacks to avoid using MRFs on Ivybridge.

Ivybridge's SEND instruction uses GRFs instead of MRFs.  Unfortunately,
a lot of our code explicitly uses MRFs, and rewriting it would take a
fair bit of effort.  In the meantime, use a hack:

- Change brw_set_dest, brw_set_src0, and brw_set_src1 to implicitly
  convert any MRFs into the top 16 GRFs.
- Enable gen6_resolve_implied_move on Ivybridge: Moving g0 to m0
  actually moves it to g111 thanks to the previous hack.

It remains to officially reserve these registers so the allocator
doesn't try to reuse them.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Eric Anholt <eric@anholt.net>