i965/fs: Make compact_virtual_grfs an optimization pass

i965/fs: Make compact_virtual_grfs an optimization pass

Previously we disabled compact_virtual_grfs when dumping optimizations.
The idea here was to make it easier to diff the dumped shader because you
didn't have a sudden renaming.  However, sometimes a bug is affected by
compact_virtual_grfs and, when this happens, you want to keep dumping
instructions with compact_virtual_grfs enabled.  By turning it into an
optimization pass and dumping it along with the others, we retain the
ability to diff because you can just diff against the compact_virtual_grf
output.

Signed-off-by: Jason Ekstrand <jason.ekstrand@intel.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>