panfrost: Fix the DISCARD_WHOLE_RES case in transfer_map()

panfrost: Fix the DISCARD_WHOLE_RES case in transfer_map()

The current implementation does not synchronize on BO readiness when
DISCARD_WHOLE_RES flag is set, which can lead to misbehaviours when the
resource being updated is being used by one of the pending or already
flushed batches.

Adding unconditional BO synchronization would do the trick, but we can
sometimes optimize this path by re-allocating a new BO instead of
waiting for the existing one to be ready.

Reported-by: Daniel Stone <daniels@collabora.com>
Reported-by: Heinrich Fink <heinrich.fink@daqri.com>
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Daniel Stone <daniels@collabora.com>
Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>