corsica: defconfig: enable some extra features

- CONFIG_RT_GROUP_SCHED is used by Android for improved scheduling
- CONFIG_KSM is a CyanogenMod feature found in Settings -> Performance
- CONFIG_CIFS as a module for those that may want to use it

Change-Id: Iaa1b8ad1655eed7fe268e1c9d2e354af0101aa1e