hwmon: (xdpe12284) Add regulator support

Add simple on/off regulator support for xdpe12284 and
other pmbus parts supported by the xdpe12284 driver.

Signed-off-by: Marcello Sylvester Bauer <sylv@sylv.io>
Link: https://lore.kernel.org/r/f69b8e7fa32cd2bad9516d8fa590abb87c7e4869.1646214248.git.sylv@sylv.io
Signed-off-by: Guenter Roeck <linux@roeck-us.net>