startup() and shutdown() hooks are called for both substreams,
so stopping either substream when another is running breaks the
latter.

E.g. playback breaks if capture is stopped when playback is running.

Move code from startup() and shutdown() to resume() and suspend()
hooks respectively to fix this issue
Signed-off-by: Vasily Khoruzhick <anarsoul@gmail.com>
Acked-by: Maxime Ripard <maxime.ripard@bootlin.com>
Signed-off-by: Mark Brown <broonie@kernel.org>