nir/algebraic: Optimize some 64-bit integer comparisons involving zero

nir/algebraic: Optimize some 64-bit integer comparisons involving zero

I noticed that we can do better for these kinds of comparisons while
working on the lowering for iadd_sat@64 and isub_sat@64.  This
eliminated 11 instruction from the fs-addSaturate-int64.shader_test.

My hope is that this will improve the run-time of int64 tests on Ice
Lake.  I have no data to support or refute this.

Unsurprisingly, no changes on shader-db.

v2: Condition the min and max patterns with nir_lower_minmax64.
Suggested by Caio.  Very long discussion in the MR. :)

Reviewed-by: Caio Marcelo de Oliveira Filho <caio.oliveira@intel.com>
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/767>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/767>