panfrost: Use modifier instead of layout throughout

panfrost: Use modifier instead of layout throughout

Instead of converting back and forth we should stick with fourcc codes
as the canonical layout definition. Furthermore modifiers allow all the
variants of AFBC to be encoded canonically, whereas the previous enum
does not (info about YTR is encoded out of band, for instance).

Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Tested-by: Icecream95 <ixn@keemail.me>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6159>