hwmon: (pmbus) Add support for TI UCD9200 series of PWM System Controllers

This patch adds hardware monitoring support for TI UCD9220, UCD9222, UCD9224,
UCD9240, UCD9244, UCD9246, and UCD9248 Digital PWM System Controllers.

Signed-off-by: Guenter Roeck <guenter.roeck@ericsson.com>
Reviewed-by: Tom Grennan <tom.grennan@ericsson.com>