nv50/ir: optimize shl(shr(a, c), c) to and(a, ~((1 << c) - 1))

nv50/ir: optimize shl(shr(a, c), c) to and(a, ~((1 << c) - 1))

Following shader-db results on GK110:

total instructions in shared programs : 6141510 -> 6131491 (-0.16%)
total gprs used in shared programs    : 910187 -> 910157 (-0.00%)
total local used in shared programs   : 15328 -> 15328 (0.00%)

                local        gpr       inst      bytes
    helped           0          18         821         821
      hurt           0           0           0           0

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