mmc: sdhci-cadence: add suspend / resume support

Currently, the probe function initializes the PHY, but PHY settings
are lost during the sleep state.  Restore the PHY registers when
resuming.

To facilitate this, split sdhci_cdns_phy_init() into the DT parse
part and PHY update part so that the latter can be invoked from the
resume hook.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>