ASoC: simple-card-utils: add asoc_simple_card_of_parse_routing()

Current simple card drivers are parsing routing on each own driver.
Encapsulation is one of simple card util's purpose.
Let's add asoc_simple_card_of_parse_routing for it.

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