mfd: Modify samsung mfd header

As Prefix of Samsung pmic changed from s5m to s2m,
To make common mfd driver for s2m and s5m series,
This patch rename header of Samsung mfd and modify mfd driver.

Signed-off-by: Sangbeom Kim <sbkim73@samsung.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>