ARM: S3C64XX: Enable power management for disk on Cragganmore

We can happily let the MMC stack do power management for the MMC card
that is our main disk on Cragganmore so let's enable it.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>