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

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 are initializing each priv,
but it is same operation.
This patch adds new asoc_simple_card_init_priv() and initialize
priv by same operation.

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