ASoC: simple-card-utils: share asoc_simple_shutdown()

The difference between simple-card / audio-graph are just using
OF graph style, or not. In other words, other things should be same.
This means, simple-card/audio-graph common functions should be
implemented at simple-card-utils, and its own functions should be
implemented at each files.

Current simple-card / audio-graph have almost same functions.
This patch shares asoc_simple_shutdown() between in these 2 drivers.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Mark Brown <broonie@kernel.org>