hwmon: (pmbus) Add support for Infineon Multi-phase xdpe122 family controllers

Add support for devices XDPE12254, XDPE12284.

All these device support two pages.
The below lists of VOUT_MODE command readout with their related VID
protocols, Digital to Analog Converter steps, supported by these
devices:
VR12.0 mode, 5-mV DAC - 0x01;
VR12.5 mode, 10-mV DAC - 0x02;
IMVP9 mode, 5-mV DAC - 0x03;
AMD mode 6.25mV - 0x10.

Signed-off-by: Vadim Pasternak <vadimp@mellanox.com>
Link: https://lore.kernel.org/r/20200113150841.17670-5-vadimp@mellanox.com
[groeck: Added missing break statement]
Signed-off-by: Guenter Roeck <linux@roeck-us.net>