i965: Use pushed UBO data in the scalar backend.

i965: Use pushed UBO data in the scalar backend.

This actually takes advantage of the newly pushed UBO data, avoiding
pull loads.

Improves performance in GLBenchmark Manhattan 3.1 by:

   HSW: ~1%, BDW/SKL/KBL GT2: 3-4%, SKL GT4: 7-8%, APL: 4-5%.
   (thanks to Eero Tamminen for these numbers)

shader-db results on Skylake, ignoring programs with spill/fill changes:

   total instructions in shared programs: 13963994 -> 13651893 (-2.24%)
   instructions in affected programs: 4250328 -> 3938227 (-7.34%)
   helped: 28527
   HURT: 0

   total cycles in shared programs: 179808608 -> 172535170 (-4.05%)
   cycles in affected programs: 79720410 -> 72446972 (-9.12%)
   helped: 26951
   HURT: 1248

   LOST:   46
   GAINED: 21

Many "Deus Ex: Mankind Divided" shaders which already spilled end up
spill a lot more (about 240 programs hurt, 9 helped).  The cycle
estimator suggests this is still overall a win (-0.23% in cycle counts)
presumably because we trade pull loads for fills.

v2: Drop "PULL" environment variable left in for initial debugging
    (caught by Matt).

Reviewed-by: Matt Turner <mattst88@gmail.com>