ASoC: rsnd: add rsnd_scu_init(), and separate init/start

ASoC: rsnd: add rsnd_scu_init(), and separate init/start

Current scu.c has rsnd_scu_start(),
and, operation of initialization/start
are implemented in this function.
This patch adds new rsnd_scu_init() and separates
rsnd_scu_start(), since rsnd_mod_ops has .init/.start callbacks.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Mark Brown <broonie@linaro.org>
(cherry picked from commit a204d90c91208d9b63ba309a1c44f582751e58c9)
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>