intel/isl: Move iris's pipe-to-isl format function to isl.

This will get reused in the shader compiler once we switch it over to pipe
formats instead of GL enums.  We can't easily deduplicate i965's
mesa-to-isl mapping because of cases like A32_FLOAT that are mapped
differently.

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3355>
3 files changed