panfrost: Update supported formats

panfrost: Update supported formats

Much of the format selection code was inherited from softpipe (!) of all
places, and a lot of it is accordingly cruft. Later if-elses were added
in random places to workaround missing formats at various points in
history. Clean up some of this.

Theoretically, any format we can texture from we can also render to. In
practice, there are a few corner cases that we need to disable
explicitly.

For one, we do have to restrict SCANOUT formats to workaround
buggy apps (in particular, dEQP which with --deqp-surface-type=window
under Weston will end up with RGB10_A2 and complain about low alpha
precision). Just be clearer about how/why.

Also, RGB5_A1 support is still broken; let's not worry about that quite
yet.

Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>