ASoC: rt715: add main capture switch and main capture volume

Add main capture switch and main capture volume control.
Main capture control has its own channel value respectivelly.

Signed-off-by: Jack Yu <jack.yu@realtek.com>
Link: https://lore.kernel.org/r/dfd43a8db04e4d52a889d6f5c1262173@realtek.com
Signed-off-by: Mark Brown <broonie@kernel.org>