power: supply: mt6370: Add MediaTek MT6370 charger driver

MediaTek MT6370 is a SubPMIC consisting of a single cell battery charger
with ADC monitoring, RGB LEDs, dual channel flashlight, WLED backlight
driver, display bias voltage supply, one general purpose LDO, and the
USB Type-C & PD controller complies with the latest USB Type-C and PD
standards.

Add support for the MediaTek MT6370 Charger driver. The charger module
of MT6370 supports High-Accuracy Voltage/Current Regulation,
Average Input Current Regulation, Battery Temperature Sensing,
Over-Temperature Protection, DPDM Detection for BC1.2.

Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: ChiaEn Wu <chiaen_wu@richtek.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>