nir/algebraic: optimize u2u32(a >> 32)

nir/algebraic: optimize u2u32(a >> 32)

fossil-db (navi21):
Totals from 352 (0.44% of 79330) affected shaders:
Instrs: 271816 -> 271240 (-0.21%); split: -0.28%, +0.07%
CodeSize: 1546520 -> 1544448 (-0.13%); split: -0.23%, +0.09%
SpillVGPRs: 832 -> 827 (-0.60%); split: -1.08%, +0.48%
Latency: 4037120 -> 4021748 (-0.38%); split: -0.41%, +0.03%
InvThroughput: 1369540 -> 1362066 (-0.55%); split: -0.59%, +0.04%
VClause: 6476 -> 6471 (-0.08%); split: -0.12%, +0.05%
SClause: 6798 -> 6794 (-0.06%)
Copies: 44828 -> 44630 (-0.44%); split: -0.89%, +0.45%
Branches: 8845 -> 8844 (-0.01%); split: -0.05%, +0.03%
PreSGPRs: 14684 -> 14659 (-0.17%)

Signed-off-by: Rhys Perry <pendingchaos02@gmail.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/25409>