regulator: rt6160: Add support for Richtek RT6160

Add support for Richtek RT6160 voltage regulator. It can provide up
to 3A output current within the adjustable voltage from 2025mV
to 5200mV. It integrate a buckboost converter to support wide input
voltage range from 2200mV to 5500mV.

Signed-off-by: ChiYuan Huang <cy_huang@richtek.com>
Link: https://lore.kernel.org/r/1622611906-2403-2-git-send-email-u0084500@gmail.com


Signed-off-by: Mark Brown <broonie@kernel.org>