i965: Optimize VUE map comparisons.

i965: Optimize VUE map comparisons.

The entire VUE map is computed based on the slots_valid bitfield;
calling brw_compute_vue_map on the same bitfield will return the
same result.  So we can simply compare those.

struct brw_vue_map is 136 bytes; doing a single 8-byte comparison is
much cheaper and should work just as well.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Chris Forbes <chrisf@ijw.co.nz>