panfrost: Defeature 24-bit textures

panfrost: Defeature 24-bit textures

mesa/st doesn't like to use 24-bit textures, preferring RGBX over true RGB even
for texture views where this isn't valid. Given how silly true RGB is in
practice, I'd rather drop support and fix texture views than go against the
grain and risk more issues down the line since nobody else in tree is testing
these paths and apps really shouldn't be caring.

Fixes page faults in arb_texture_view-rendering-formats_gles3 which tries to
sample an R8G8B8_UINT texture with a R8G8B8X8_UNORM view in one subcase. That
test is now passing reliably.

Signed-off-by: Alyssa Rosenzweig <alyssa@collabora.com>
Reviewed-by: Emma Anholt <emma@anholt.net>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Cc: mesa-stable
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/21891>