mfd: Add S5M core driver

S5M series are pmic including mutiple functional devices.
It can support PMIC, RTC, Battery charger, codec.
This patch implement core driver for s5m series.

Signed-off-by: Sangbeom Kim <sbkim73@samsung.com>
Reviewed-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>