nir: Rename nir_instr_type_ssa_undef to nir_instr_type_undef

nir: Rename nir_instr_type_ssa_undef to nir_instr_type_undef

We already renamed the type, we just need to rename the enum and the
casting helper functions.

Generated with sed:

    sed -i -e 's/nir_instr_type_ssa_undef/nir_instr_type_undef/g' src/**/*.h src/**/*.c src/**/*.cpp
    sed -i -e 's/nir_instr_as_ssa_undef/nir_instr_as_undef/g' src/**/*.h src/**/*.c src/**/*.cpp

and two tiny whitespace fixups in lima.

Reviewed-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/24703>