nir/algebraic: add patterns for a >> #b << #b

nir/algebraic: add patterns for a >> #b << #b

Fixes compilation of a Battlefront 2 shader with ACO by removing VGPR
spilling. The reassociation makes it worse on LLVM though.

pipeline-db (ACO):
Totals from affected shaders:
SGPRS: 10704 -> 10688 (-0.15 %)
VGPRS: 18736 -> 18528 (-1.11 %)
Spilled SGPRs: 70 -> 70 (0.00 %)
Spilled VGPRs: 0 -> 0 (0.00 %)
Private memory VGPRs: 0 -> 0 (0.00 %)
Scratch size: 0 -> 0 (0.00 %) dwords per thread
Code Size: 909696 -> 885796 (-2.63 %) bytes
LDS: 225 -> 225 (0.00 %) blocks
Max Waves: 1115 -> 1129 (1.26 %)

pipeline-db (LLVM):
Totals from affected shaders:
SGPRS: 8472 -> 8424 (-0.57 %)
VGPRS: 14284 -> 14368 (0.59 %)
Spilled SGPRs: 0 -> 0 (0.00 %)
Spilled VGPRs: 442 -> 503 (13.80 %)
Private memory VGPRs: 0 -> 0 (0.00 %)
Scratch size: 268 -> 396 (47.76 %) dwords per thread
Code Size: 862568 -> 853028 (-1.11 %) bytes
LDS: 0 -> 0 (0.00 %) blocks
Max Waves: 971 -> 964 (-0.72 %)

Signed-off-by: Rhys Perry <pendingchaos02@gmail.com>
Reviewed-by: Connor Abbott <cwabbott0@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/2271>