panfrost: LogicOp fixes and non 8-bit format support

panfrost: LogicOp fixes and non 8-bit format support

With the previous LogicOp commit almost half of the blend modes were
broken because the surplus bits were not cleared after an inot.

v2:
 - Remove u8 "fast path" as 8-bit is not well optimised yet
 - Don't mask for 32-bit formats as that triggers an assert

Fixes: 068806c9f6b ("panfrost: LogicOp support")
Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/3943>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/3943>