nir: Add new instructions for INTEL_shader_integer_functions2

nir: Add new instructions for INTEL_shader_integer_functions2

uctz isn't added because it will implemented in the GLSL path and the
SPIR-V path using other pre-existing instructions.

v2: Avoid signed integer overflow for uabs_isub(0, INT_MIN).  Noticed by
Caio.

v3: Alternate fix for signed integer overflow for abs_sub(0, INT_MIN).
I tried the previous methon in a small test program with -ftrapv, and it
failed.

Reviewed-by: Caio Marcelo de Oliveira Filho <caio.oliveira@intel.com> [v1]
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/767>