intel/vec4: Add support for UBO pushing

Shader-db results on Haswell (vec4 only):

total instructions in shared programs: 2853928 -> 2726576 (-4.46%)
instructions in affected programs: 855840 -> 728488 (-14.88%)
helped: 9500
HURT: 18
helped stats (abs) min: 1 max: 359 x̄: 13.54 x̃: 11
helped stats (rel) min: 0.44% max: 53.33% x̄: 19.13% x̃: 17.44%
HURT stats (abs)   min: 4 max: 124 x̄: 71.00 x̃: 92
HURT stats (rel)   min: 3.64% max: 77.86% x̄: 46.43% x̃: 52.12%
95% mean confidence interval for instructions value: -13.78 -12.98
95% mean confidence interval for instructions %-change: -19.21% -18.81%
Instructions are helped.

total cycles in shared programs: 101822616 -> 60245580 (-40.83%)
cycles in affected programs: 93312382 -> 51735346 (-44.56%)
helped: 13292
HURT: 4506
helped stats (abs) min: 2 max: 1229260 x̄: 3370.82 x̃: 776
helped stats (rel) min: 0.04% max: 96.70% x̄: 47.56% x̃: 43.76%
HURT stats (abs)   min: 2 max: 17644 x̄: 716.37 x̃: 82
HURT stats (rel)   min: 0.02% max: 491.80% x̄: 41.00% x̃: 11.11%
95% mean confidence interval for cycles value: -3037.07 -1635.03
95% mean confidence interval for cycles %-change: -26.03% -24.25%
Cycles are helped.

total spills in shared programs: 1080 -> 1314 (21.67%)
spills in affected programs: 74 -> 308 (316.22%)
helped: 0
HURT: 47

total fills in shared programs: 310 -> 497 (60.32%)
fills in affected programs: 71 -> 258 (263.38%)
helped: 0
HURT: 47

total sends in shared programs: 239884 -> 151799 (-36.72%)
sends in affected programs: 129302 -> 41217 (-68.12%)
helped: 9547
HURT: 0
helped stats (abs) min: 1 max: 226 x̄: 9.23 x̃: 8
helped stats (rel) min: 3.12% max: 98.15% x̄: 72.38% x̃: 80.00%
95% mean confidence interval for sends value: -9.48 -8.98
95% mean confidence interval for sends %-change: -72.80% -71.97%
Sends are helped.

cc @airlied