hwmon: (pmbus/adm1275) Add support for ADM1276

ADM1276 is mostly compatible to ADM1275, with added support for input power
measurement. Add support for it to the ADM1275 driver.

Signed-off-by: Guenter Roeck <guenter.roeck@ericsson.com>
Acked-by: Jean Delvare <khali@linux-fr.org>