pan/bi: Add bi_bytemask_of_read_components helpers

Same purpose as the Midgard version, but the implementation is
*dramatically* simpler thanks to our more regular IR.

Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4150>
2 files changed