nir/algebraic: always lower idiv to shifts if bitops are allowed

nir/algebraic: always lower idiv to shifts if bitops are allowed

why would you want anything else

The only platform significantly affected by this is Intel where `lower_idiv`
is not set today but neither is `lower_bitops`.  There it seems to still be
a boon over-all.

Shader-db results on Ice Lake:

    total instructions in shared programs: 19719051 -> 19735766 (0.08%)
    instructions in affected programs: 106992 -> 123707 (15.62%)
    helped: 0
    HURT: 445
    HURT stats (abs)   min: 3 max: 295 x̄: 37.56 x̃: 44
    HURT stats (rel)   min: 0.16% max: 33.33% x̄: 19.60% x̃: 19.38%
    95% mean confidence interval for instructions value: 33.60 41.53
    95% mean confidence interval for instructions %-change: 18.97% 20.23%
    Instructions are HURT.

    total loops in shared programs: 5973 -> 5973 (0.00%)
    loops in affected programs: 0 -> 0
    helped: 0
    HURT: 0

    total cycles in shared programs: 489405810 -> 486917482 (-0.51%)
    cycles in affected programs: 4759097 -> 2270769 (-52.29%)
    helped: 406
    HURT: 34
    helped stats (abs) min: 2 max: 64661 x̄: 6291.95 x̃: 3126
    helped stats (rel) min: 0.02% max: 79.42% x̄: 43.32% x̃: 55.83%
    HURT stats (abs)   min: 2 max: 29376 x̄: 1947.12 x̃: 30
    HURT stats (rel)   min: 0.04% max: 23.82% x̄: 4.66% x̃: 1.33%
    95% mean confidence interval for cycles value: -6753.06 -4557.52
    95% mean confidence interval for cycles %-change: -42.60% -36.63%
    Cycles are helped.

    total spills in shared programs: 12481 -> 12482 (<.01%)
    spills in affected programs: 47 -> 48 (2.13%)
    helped: 0
    HURT: 1

    total fills in shared programs: 12816 -> 12819 (0.02%)
    fills in affected programs: 71 -> 74 (4.23%)
    helped: 0
    HURT: 1

    total sends in shared programs: 1010124 -> 1010124 (0.00%)
    sends in affected programs: 0 -> 0
    helped: 0
    HURT: 0

    LOST:   1
    GAINED: 0

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6963>