mmc: sdhci-of-dwcmshc: Add runtime PM operations

This commit implements the runtime PM operations to disable eMMC card clock
when idle.

Reviewed-by: David Thompson <davthompson@nvidia.com>
Signed-off-by: Liming Sun <limings@nvidia.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Link: https://lore.kernel.org/r/20230822195929.168552-2-limings@nvidia.com


Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>