i915: Use nir_group_loads() to reduce texture indirection phases.

i915: Use nir_group_loads() to reduce texture indirection phases.

total instructions in shared programs: 467049 -> 467040 (<.01%)
instructions in affected programs: 573 -> 564 (-1.57%)

total tex_indirect in shared programs: 14133 -> 14019 (-0.81%)
tex_indirect in affected programs: 491 -> 377 (-23.22%)

total temps in shared programs: 28543 -> 29178 (2.22%)
temps in affected programs: 3307 -> 3942 (19.20%)

LOST:   0
GAINED: 65
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/25533>