panfrost: Make sure a clear does not re-use a pre-existing batch

panfrost: Make sure a clear does not re-use a pre-existing batch

glClear()s are expected to be the first thing GL apps do before drawing
new things. If there's already an existing batch targetting the same
FBO that has draws attached to it, we should make sure the new clear
gets a new batch assigned to guaranteed that the FB content is actually
cleared with the requested color/depth/stencil values.

We create a panfrost_get_fresh_batch_for_fbo() helper for that and
call it from panfrost_clear().

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