ASoC: rt5670: add API to select ASRC clock source

When codec is in slave mode, ASRC can suppress noise for asynchronous
MCLK and LRCLK or special I2S format. This patch defines an API to select
the clock source for specified filters.  And the codec driver will turn on ASRC
for these filters if ASRC is selected as their clock source.

Signed-off-by: Bard Liao <bardliao@realtek.com>
Signed-off-by: Mengdong Lin <mengdong.lin@intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>