nir: Rewrite lower_clip_cull_distance_arrays to do a lot less lowering

nir: Rewrite lower_clip_cull_distance_arrays to do a lot less lowering

Instead of going to all the work of to combine them into one array, just
make two arrays and use location_frac to colocate them within CLIP0.
Then the back-end can sort things out and stack them on top of each
other.  Thanks to ef99f4c8, we also don't need to set compact anymore.

Reviewed-by: Alejandro Piñeiro <apinheiro@igalia.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>