panfrost: Move mir_to_bytemask to common code

...also so we can start sharing code properly between the panfrost
compilers.

Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4139>
10 files changed