i965: Enable nir_opt_idiv_const for 32 and 64-bit integers

i965: Enable nir_opt_idiv_const for 32 and 64-bit integers

The pass should work for all bit sizes but it's less clear that the
extra instructions are worth it on small integers.  Also, the hardware
doesn't do mul_high on anything other than 32-bit integers and, absent
any decent mechanism for testing the pass on 8 and 16-bit types, it's
probably best to just leave it disabled for now.

Shader-db results on Sky Lake:

    total instructions in shared programs: 15105795 -> 15111403 (0.04%)
    instructions in affected programs: 72774 -> 78382 (7.71%)
    helped: 0
    HURT: 265

Note that hurt here actually means helped because we're getting rid of
integer quotient operations (which are a send on some platforms!) and
replacing them with fairly cheap ALU ops.

Reviewed-by: Ian Romanick ian.d.romanick@intel.com