nir/algebraic: optimize bcsel(a, 0, 1) to b2i

nir/algebraic: optimize bcsel(a, 0, 1) to b2i

This avoids combination with other bcsel operations,
and as b2i is often a no-op (when used for iadd and such),
the resulting pattern is preferable.

Totals from affected shaders: (VEGA)
SGPRS: 598448 -> 598448 (0.00 %)
VGPRS: 457940 -> 457352 (-0.13 %)
Spilled SGPRs: 127154 -> 127154 (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: 64836352 -> 64802728 (-0.05 %) bytes
LDS: 781 -> 781 (0.00 %) blocks
Max Waves: 22931 -> 22931 (0.00 %)

Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Reviewed-by: Rhys Perry <pendingchaos02@gmail.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4830>