panfrost: Add a blendable format table

panfrost: Add a blendable format table

Map PIPE formats that are fixed-function blendable to their (internal,
writeback) tuple. Formats which are renderable but require a blend
shadeer will be handled elsewhere to keep this easy to verify.

Notice the subset of SFBD and MFBD color writeback formats used to
identify fixed-function blendable formats are bit compatible, so it
suffices to store only the MFBD variants.

Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Tested-by: Christian Hewitt <christianshewitt@gmail.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7352>