nvc0/ir: treat FMA like MAD for operand propagation

nvc0/ir: treat FMA like MAD for operand propagation

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

shader-db changes:
total instructions in shared programs : 3901147 -> 3842505 (-1.50%)
total gprs used in shared programs    : 471258 -> 467359 (-0.83%)
total local used in shared programs   : 27405 -> 27361 (-0.16%)
total bytes used in shared programs   : 35749888 -> 35214176 (-1.50%)

                local        gpr       inst      bytes
    helped          17        1829        4091        4091
      hurt           4          44           3           3

Signed-off-by: Karol Herbst <karolherbst@gmail.com>
Reviewed-by: Ilia Mirkin <imirkin@alum.mit.edu>
Cc: mesa-stable@lists.freedesktop.org