ASoC: rsnd: add Synchronous SRC mode

Renesas R-Car sound SRC (= Sampling Rate Converter) has
Asynchronous/Synchronous SRC mode. Asynchronous mode is already
supported via DPCM. This patch adds Synchronous mode on it.

The condition of enabling Synchronous mode are
- SoC is clock master
- Sound uses SRC
- Sound doesn't use DVC
- Sound card uses DPCM (= rsrc-card card)

	amixer set "SRC Out Rate" on
	aplay xxx.wav &
	amixer set "SRC Out Rate" 48000

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