panfrost: Don't freeze blit batches

panfrost: Don't freeze blit batches

We don't want blit batches to interfere with subsequent draw calls, but
we want to keep them in the list of pending batches (so they gets flushed
when glFlush() is called), so calling panfrost_freeze_batch() is not an
option. Reset the ctx->batch pointer manually.

Note that there's no risk to have those batches re-used to queue
unrelated draws because we created a unique pipe_surface object per
blit call, and the batch logic use the surface pointers to calculate
the batch key hash.

Fixes: e1649e916d67 ("panfrost: Use pan_blit() when PAN_MESA_DEBUG=panblit")
Reported-by: Icecream95 <ixn@disroot.org>
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Tested-by: Icecream95 <ixn@disroot.org>
Reviewed-by:  Alyssa Rosenzweig <alyssa@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/10842>