hwmon: (pmbus) Add support for ADM1266

Add pmbus probing driver for the adm1266 Cascadable
Super Sequencer with Margin Control and Fault Recording.
Driver is using the pmbus_core, creating sysfs files
under hwmon for inputs: vh1->vh4 and vp1->vp13.

Signed-off-by: Alexandru Tachici <alexandru.tachici@analog.com>
Link: https://lore.kernel.org/r/20200812142055.9213-2-alexandru.tachici@analog.com
[groeck: Use .probe_new function, adjust for changed pmbus_do_probe API]
Signed-off-by: Guenter Roeck <linux@roeck-us.net>