nir: update nir_is_supported_terminator_condition()

nir: update nir_is_supported_terminator_condition()

Ever since 4246c2869c3c and 7d85dc4f350b loop unrolling can no
longer depend on inot being eliminated from the loop
terminator condition so we need to be able to handle it.

Here we simply check to see if the inot contains a simple
terminator condition we previously handled. We also update
the previous users of this function to use a newly name
copy of the previous behaviour
nir_is_terminator_condition_with_two_inputs().

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/18006>