panfrost: Move the batch submission logic to panfrost_batch_submit()

panfrost: Move the batch submission logic to panfrost_batch_submit()

We are about to patch panfrost_flush() to flush all pending batches,
not only the current one. In order to do that, we need to move the
'flush single batch' code to panfrost_batch_submit().

While at it, we get rid of the existing pipelining logic, which is
currently unused and replace it by an unconditional wait at the end of
panfrost_batch_submit(). A new pipeline logic will be introduced later
on.

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