radeonsi: use LRP from gallivm

radeonsi: use LRP from gallivm

Totals:
SGPRS: 344552 -> 344368 (-0.05 %)
VGPRS: 197132 -> 197552 (0.21 %)
Code Size: 7375376 -> 7366304 (-0.12 %) bytes
LDS: 91 -> 91 (0.00 %) blocks
Scratch: 1679360 -> 1615872 (-3.78 %) bytes per wave

Totals from affected shaders:
SGPRS: 47736 -> 47552 (-0.39 %)
VGPRS: 27952 -> 28372 (1.50 %)
Code Size: 1392724 -> 1383652 (-0.65 %) bytes
LDS: 39 -> 39 (0.00 %) blocks
Scratch: 513024 -> 449536 (-12.38 %) bytes per wave

Reviewed-by: Michel Dänzer <michel.daenzer@amd.com>