ac: reassociate FP expressions for inexact instructions for radeonsi

ac: reassociate FP expressions for inexact instructions for radeonsi

Totals:
SGPRS: 2591784 -> 2590696 (-0.04 %)
VGPRS: 1666888 -> 1666736 (-0.01 %)
Spilled SGPRs: 4131 -> 4107 (-0.58 %)
Spilled VGPRs: 38 -> 38 (0.00 %)
Private memory VGPRs: 2176 -> 2176 (0.00 %)
Scratch size: 2228 -> 2228 (0.00 %) dwords per thread
Code Size: 52715468 -> 52693584 (-0.04 %) bytes
LDS: 92 -> 92 (0.00 %) blocks
Max Waves: 479897 -> 479892 (-0.00 %)
Wait states: 0 -> 0 (0.00 %)

Reviewed-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4696>