This patch adds device driver of Richtek PMIC.
The driver support battery fuel gauge. Fuel gauge calculates and determines the
battery state of charge (SOC) according to battery open circuit voltage (OCV).
Also, this driver provides battery average voltage, voltage and battery present
property.

Cc: Sebastian Reichel <sre@kernel.org>
Cc: Dmitry Eremin-Solenikov <dbaryshkov@gmail.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Signed-off-by: Beomho Seo <beomho.seo@samsung.com>
Acked-by: Chanwoo Choi <cw00.choi@samsung.com>
Signed-off-by: Sebastian Reichel <sre@kernel.org>