ac/nir/nggc: Only repack arguments that are needed.

ac/nir/nggc: Only repack arguments that are needed.

Don't repack everything, only what is actually used.
The goal of this commit is primarily to remove unnecessary
LDS stores and loads. In addition to that, it also gets rid of
a few VALU instructions and reduces VGPR use.

Fossil DB stats on Sienna Cichlid with NGGC on:

Totals from 6951 (5.40% of 128647) affected shaders:
VGPRs: 206056 -> 205360 (-0.34%); split: -0.79%, +0.45%
CodeSize: 12344568 -> 12269312 (-0.61%); split: -0.62%, +0.01%
MaxWaves: 211206 -> 212196 (+0.47%)
Instrs: 2319459 -> 2308483 (-0.47%); split: -0.50%, +0.03%
Latency: 7220829 -> 7164721 (-0.78%); split: -1.21%, +0.43%
InvThroughput: 1051450 -> 1049191 (-0.21%); split: -0.36%, +0.15%
VClause: 25794 -> 25445 (-1.35%); split: -1.97%, +0.61%
SClause: 39192 -> 39277 (+0.22%); split: -0.21%, +0.43%
Copies: 315756 -> 313404 (-0.74%); split: -1.17%, +0.42%
Branches: 127878 -> 127879 (+0.00%); split: -0.00%, +0.00%
PreVGPRs: 168029 -> 160162 (-4.68%)

Signed-off-by: Timur Kristóf <timur.kristof@gmail.com>
Reviewed-by: Daniel Schürmann <daniel@schuermann.dev>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/12246>