nir: Use SM5 properties to optimize shift(a@32, iand(31, b))

nir: Use SM5 properties to optimize shift(a@32, iand(31, b))

This is a common pattern from HLSL->SPIRV translation
and supported in HW by all current NIR backends.

vkpipeline-db results anv (SKL):

    total instructions in shared programs: 6403130 -> 6402380 (-0.01%)
    instructions in affected programs: 204084 -> 203334 (-0.37%)
    helped: 208
    HURT: 0

    total cycles in shared programs: 1915629582 -> 1918198408 (0.13%)
    cycles in affected programs: 1158892682 -> 1161461508 (0.22%)
    helped: 107
    HURT: 86

shader-db results on i965 (KBL):

    total instructions in shared programs: 15284592 -> 15284568 (<.01%)
    instructions in affected programs: 81683 -> 81659 (-0.03%)
    helped: 24
    HURT: 0

    total cycles in shared programs: 375013622 -> 375013932 (<.01%)
    cycles in affected programs: 40169618 -> 40169928 (<.01%)
    helped: 13
    HURT: 9

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>