mfd: rt5033: Add Richtek RT5033 driver core.

This patch adds a new driver for Richtek RT5033 driver.
RT5033 is a Multifunction device which includes battery charger, fuel gauge,
flash LED current source, LDO and synchronous Buck converter. It is interfaced
to host controller using I2C interface.

Signed-off-by: Beomho Seo <beomho.seo@samsung.com>
Acked-by: Chanwoo Choi <cw00.choi@samsung.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>