panfrost: Use a pipe_framebuffer_state as the batch key

panfrost: Use a pipe_framebuffer_state as the batch key

This way we have all the fb_state information directly attached to a
batch and can pass only the batch to functions emitting CMDs, which is
needed if we want to be able to queue CMDs to a batch that's not
currently bound to the context.

Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>