mmc: sdhci-esdhc-imx: add esdhc specific suspend resume callback

It will be used for platform specific suspend/resume state save/restore
work for some low power mode like Mega/Fast or LPSR mode.

Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Dong Aisheng <aisheng.dong@nxp.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>