nir: Optimize integer division and modulus with 1

nir: Optimize integer division and modulus with 1

The previous power-of-two rules didn't catch idiv (because i965 doesn't
set lower_idiv) and imod cases.  The udiv and umod cases should have
been caught, but I included them for orthogonality.

This fixes silly code observed from compute shaders with local_size_[xy]
= 1.

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=98299
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>