power: supply: rt9467: Add Richtek RT9467 charger driver

RT9467 is a switch-mode single cell Li-Ion/Li-Polymer battery charger
for portable applications.

It integrates a synchronous PWM controller, power MOSFETs,
input current sensing and regulation, high-accuracy voltage regulation,
and charge termination. The charge current is regulated through
integrated sensing resistors.

The RT9467 also features USB On-The-Go (OTG) support. It also integrates
D+/D- pin for USB host/charging port detection.

Co-developed-by: ChiYuan Huang <cy_huang@richtek.com>
Signed-off-by: ChiYuan Huang <cy_huang@richtek.com>
Signed-off-by: ChiaEn Wu <chiaen_wu@richtek.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>