regulator: Add S5M8767A regulator driver

S5M8767A is a cost-effective PMIC which is designed for mobile applications.
It includes high efficient 9 Buck converters, 28 LDOs.
Especially, S5M8767A is optimized for Multi-core SOCs.
And during DVFS operation, S5M8767A output stable voltage.
This patch implement regulator driver for S5M8767A.
Signed-off-by: NSangbeom Kim <sbkim73@samsung.com>
Signed-off-by: NMark Brown <broonie@opensource.wolfsonmicro.com>