panfrost/ci: Split rules by ISA

panfrost/ci: Split rules by ISA

Panfrost has two compilers, one for Midgard GPUs and one for Bifrost
GPUs. The respective compilers are src/panfrost/midgard and
src/panfrost/bifrost. Changes internal to just one compiler (or
disassembler) cannot affect the other hardware, so there's no need to
run extra jobs in these cases.

Also split out common vs Gallium panfrost so we can do the right thing
for panvk builds in the imminent future.

Signed-off-by: Alyssa Rosenzweig <alyssa@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/10924>