nir/flrp: Fix flrp(±1, b, c) lowering path
This the error in the flrp(±1, b, c) lowering path and try to fix most of the shader-db regressions caused by the fix.
Piglit test is at piglit!52 (merged).
Still running through Intel CI, but tests run locally with lower_flrp32
force on look good.
Edited by Ian Romanick