Avoid flushing the submission queue (of others) under the client's
timeline lock, but instead move it to the end so that we may catch more.

References: https://gitlab.freedesktop.org/drm/intel/-/issues/1066Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200420125356.26614-2-chris@chris-wilson.co.uk