panfrost: Take into account flags when looking up in the BO cache

panfrost: Take into account flags when looking up in the BO cache

This will be useful right now so we avoid retrieving a non-executable
buffer when a executable one is needed.

As we support more flags, this logic will need to be extended to
consider the different trade-offs to be made when matching BO
specifications to BOs in the cache.

Signed-off-by: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>