nv50/ir: also do PostRaLoadPropagation for FMA

nv50/ir: also do PostRaLoadPropagation for FMA

Helps Feral-ported games, due to their use of fma()

shader-db changes:
total instructions in shared programs : 3934925 -> 3934327 (-0.02%)
total gprs used in shared programs    : 481563 -> 481563 (0.00%)
total local used in shared programs   : 27469 -> 27469 (0.00%)
total bytes used in shared programs   : 36061888 -> 36056504 (-0.01%)

                local        gpr       inst      bytes
    helped           0           0         228         228
      hurt           0           0           0           0

Signed-off-by: Karol Herbst <karolherbst@gmail.com>
Reviewed-by: Ilia Mirkin <imirkin@alum.mit.edu>