PM subsystem treats mmc card as removed during suspend.

If MMC is used to store the root file system, it is better to tell the kernel
not to treat it as a removable media, so select CONFIG_MMC_UNSAFE_RESUME for
such purpose.
Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>