aco: use v_fma_mix for f2f32 and f2f16 on gfx11 if wave64

v_fma_mix can be dual issued, trade some code size for throughput.

Foz-DB GFX1100:
Totals from 8204 (6.08% of 134864) affected shaders:
CodeSize: 89608584 -> 89693968 (+0.10%)
Latency: 160744811 -> 160699309 (-0.03%); split: -0.03%, +0.00%
InvThroughput: 19737977 -> 19678308 (-0.30%)

Reviewed-by: Rhys Perry <pendingchaos02@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/21402>