aco/gfx11: support vinterp as fma_mix

aco/gfx11: support vinterp as fma_mix

Totals from 718 (0.94% of 76572) affected shaders:
Instrs: 657897 -> 654219 (-0.56%)
CodeSize: 3471668 -> 3457352 (-0.41%); split: -0.41%, +0.00%
VGPRs: 34200 -> 34164 (-0.11%)
Latency: 11687698 -> 11677030 (-0.09%); split: -0.10%, +0.00%
InvThroughput: 1455371 -> 1451537 (-0.26%); split: -0.26%, +0.00%
VClause: 7598 -> 7600 (+0.03%)
SClause: 18293 -> 18241 (-0.28%); split: -0.44%, +0.15%
Copies: 34641 -> 34644 (+0.01%); split: -0.05%, +0.06%

Reviewed-by: Rhys Perry <pendingchaos02@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/25220>