power_supply: Add driver for MAX8903 charger

MAX8903 is an integrated battery charger and selector with two
power inputs (USB and AC adapter). This driver enables the charger,
handles interrupts, and provides power-supply-class information to
userland.

Tested on Exynos4 NURI / S5PC210 SLP7 boards.

Signed-off-by: MyungJoo Ham <myungjoo.ham@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Anton Vorontsov <cbouatmailru@gmail.com>