nir/algebraic: Recognize open-coded flrp(a, b, fsat(c))

nir/algebraic: Recognize open-coded flrp(a, b, fsat(c))

All Gen6+ GPUs had similar results. (Skylake shown)
total instructions in shared programs: 15336712 -> 15336622 (<.01%)
instructions in affected programs: 3952 -> 3862 (-2.28%)
helped: 24
HURT: 0
helped stats (abs) min: 3 max: 5 x̄: 3.75 x̃: 4
helped stats (rel) min: 1.75% max: 2.70% x̄: 2.34% x̃: 2.46%
95% mean confidence interval for instructions value: -4.06 -3.44
95% mean confidence interval for instructions %-change: -2.47% -2.22%
Instructions are helped.

total cycles in shared programs: 355722052 -> 355721235 (<.01%)
cycles in affected programs: 27326 -> 26509 (-2.99%)
helped: 20
HURT: 4
helped stats (abs) min: 1 max: 227 x̄: 44.75 x̃: 14
helped stats (rel) min: 0.12% max: 22.95% x̄: 3.83% x̃: 1.23%
HURT stats (abs)   min: 2 max: 64 x̄: 19.50 x̃: 6
HURT stats (rel)   min: 0.21% max: 3.63% x̄: 1.24% x̃: 0.55%
95% mean confidence interval for cycles value: -61.61 -6.47
95% mean confidence interval for cycles %-change: -5.59% -0.39%
Cycles are helped.

No changes on Ice Lake, Iron Lake, or GM45.

Reviewed-by: Matt Turner <mattst88@gmail.com>