ASoC: mchp-spdiftx: add runtime pm support

Add runtime PM support for Microchip SPDIFTX driver. The runtime PM
APIs disables/enables IP's clock and enables/disable caching for
regmap.

Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Link: https://lore.kernel.org/r/20221117123750.291911-3-claudiu.beznea@microchip.com


Signed-off-by: Mark Brown <broonie@kernel.org>