regulator: Add support for Richtek RT5739 voltage regulator

The RT5739 is a step-down switching voltage regulator that supports
output voltage ragne from 300mV to 1300mV with the wide input supply
voltage range from 2.5V to 5.5V.

Signed-off-by: ChiYuan Huang <cy_huang@richtek.com>
Link: https://lore.kernel.org/r/1676599618-24819-3-git-send-email-cy_huang@richtek.com


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