radv: use lower_ballot_bit_count_to_mbcnt_amd

radv: use lower_ballot_bit_count_to_mbcnt_amd

Foz-DB Navi21:
Totals from 62 (0.05% of 134864) affected shaders:
VGPRs: 2464 -> 2440 (-0.97%)
CodeSize: 332408 -> 324276 (-2.45%)
MaxWaves: 1690 -> 1692 (+0.12%)
Instrs: 62356 -> 60828 (-2.45%)
Latency: 595723 -> 592554 (-0.53%)
InvThroughput: 126106 -> 124241 (-1.48%)
SClause: 2163 -> 2162 (-0.05%)
Copies: 6392 -> 6226 (-2.60%); split: -2.94%, +0.34%
Branches: 2295 -> 2298 (+0.13%)
PreSGPRs: 2390 -> 2389 (-0.04%)
PreVGPRs: 2139 -> 2117 (-1.03%); split: -1.08%, +0.05%

Reviewed-by: Rhys Perry <pendingchaos02@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/22783>