mmc: sdhci-esdhc-imx: Enable/Disable mmc clock during runtime suspend

mmc clock can be stopped during runtime suspend and restart during runtime
resume if the sdio irq is not enabled. Stop sdio clock reduce EMI of
the device when the bus is not in use.

Signed-off-by: Michael Trimarchi <michael@amarulasolutions.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>