ASoC: mchp-spdifrx: add runtime pm support

Add runtime PM support for Microchip SPDIFRX driver. On runtime suspend
the clocks are disabled and regmap is set in caching mode. On runtime
resume the clocks are enabled and regmap is synced with the device.
Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Link: https://lore.kernel.org/r/20230130120647.638049-8-claudiu.beznea@microchip.comSigned-off-by: Mark Brown <broonie@kernel.org>