i965/vs: Use the sampler for VS pull constant loading on Ivybridge.

i965/vs: Use the sampler for VS pull constant loading on Ivybridge.

Substantially increases performance in GLBenchmark PRO:
- 320x240   => 3.28x
- 1920x1080 => 1.47x
- 2560x1440 => 1.27x

The LD message ignores the sampler unit index and SAMPLER_STATE pointer,
instead relying on hard-wired default state.  Thus, there's no need to
worry about running out of sampler units or providing SAMPLER_STATE;
this small patch should be all that's required.

NOTE: This is a candidate for release branches.
      (It requires the preceding commit to compile.)

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