radeonsi/nir: call some more var optimisation passes

radeonsi/nir: call some more var optimisation passes

shader-db results (VEGA64):

Totals from affected shaders:
SGPRS: 5328912 -> 5329680 (0.01 %)
VGPRS: 2969308 -> 2969164 (-0.00 %)
Spilled SGPRs: 37921 -> 37917 (-0.01 %)
Spilled VGPRs: 32882 -> 29024 (-11.73 %)
Private memory VGPRs: 0 -> 0 (0.00 %)
Scratch size: 1400 -> 1200 (-14.29 %) dwords per thread
Code Size: 121126000 -> 121282784 (0.13 %) bytes
LDS: 1501 -> 1501 (0.00 %) blocks
Max Waves: 933188 -> 933229 (0.00 %)
Wait states: 0 -> 0 (0.00 %)

Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>