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

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

No shader-db changes Ice Lake, Iron Lake, or GM45 as these platforms
lack a LRP instruction.

v2: Remove flrp@64 cases.  Since Gen11 removes flrp@32, it seems
unlikely that we'll ever have a flrp@64.  Should that occur, the cases
can be added back.

All Gen6-Gen9 platforms had similar results. (Skylake shown)
total instructions in shared programs: 15041996 -> 15041184 (<.01%)
instructions in affected programs: 71776 -> 70964 (-1.13%)
helped: 312
HURT: 0
helped stats (abs) min: 2 max: 3 x̄: 2.60 x̃: 3
helped stats (rel) min: 0.36% max: 4.55% x̄: 1.75% x̃: 1.28%
95% mean confidence interval for instructions value: -2.66 -2.55
95% mean confidence interval for instructions %-change: -1.89% -1.61%
Instructions are helped.

total cycles in shared programs: 354303333 -> 354301807 (<.01%)
cycles in affected programs: 433742 -> 432216 (-0.35%)
helped: 206
HURT: 78
helped stats (abs) min: 2 max: 244 x̄: 21.02 x̃: 8
helped stats (rel) min: 0.06% max: 19.59% x̄: 1.72% x̃: 0.82%
HURT stats (abs)   min: 1 max: 220 x̄: 35.95 x̃: 10
HURT stats (rel)   min: 0.07% max: 30.48% x̄: 2.53% x̃: 0.56%
95% mean confidence interval for cycles value: -10.68 -0.06
95% mean confidence interval for cycles %-change: -0.99% -0.12%
Cycles are helped.

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