ASoC: soc-core: add soc_component_to_node()

Many function are getting device_node from component
with caring its parent component.
This patch adds new soc_component_to_node() and share
same code.

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