zink: move scanout sync to end of batch

zink: move scanout sync to end of batch

this is called from the non-deferred flush path, which means it should always
be triggering work, which means it will always result in a queue submission

instead of relying on the pipe_context::flush hook to be triggered, which is
not a guarantee, do scanout sync during queue submission to ensure that scanout
objects are always in sync

Fixes: 104603fa763 ("zink: create separate linear tiling image for scanout")

Reviewed-by: Adam Jackson <ajax@redhat.com>
Acked-by: Erik Faye-Lund <erik.faye-lund@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/10358>