mmc: mmci: Put the device into low power state at system suspend

For CONFIG_PM_SLEEP, the device were always left in full power state
after system suspend.

We solely relied on a power domain to put it into low power state,
which is an unreasonable requirement to put on SOCs to implement.
Especially for those SOCs not supporting power domains at all.

Use pm_runtime_force_suspend|resume() as the system suspend callbacks,
to resolve the issue.

Cc: Russell King <linux@arm.linux.org.uk>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>