nir: Add a flag for lowering fsqrt(x) to frcp(frsqrt(x)).

vc4 cse/algebraic-disabled stats:
total uniforms in shared programs: 13972 -> 13966 (-0.04%)
uniforms in affected programs:     408 -> 402 (-1.47%)
total instructions in shared programs: 44973 -> 44911 (-0.14%)
instructions in affected programs:     1551 -> 1489 (-4.00%)

v2: Rebase to master (no TGSI->NIR present)

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org> (v1)
2 files changed