hwmon: (pmbus/isl68137) Add support for RAA229621

The RAA229621 is a digital dual output multiphase (X+Y <= 8) PWM controller
designed to be compliant with AMD SVI3 specifications, targeting VDDCR_CPU
and VDDCR_SOC rails.

Add support for it to the isl68137 driver.

Signed-off-by: Chiang Brian <chiang.brian@inventec.com>
Link: https://lore.kernel.org/r/20250605040134.4012199-3-chiang.brian@inventec.com


Signed-off-by: Guenter Roeck <linux@roeck-us.net>