hwmon: (pmbus) Add support for Texas Instruments tps53679 device

The below lists of VOUT_MODE command readout with their related VID
protocols, Digital to Analog Converter steps, supported by the device:
VR12.0 mode, 5-mV DAC - 0x21
VR12.5 mode, 10-mV DAC - 0x22
VR13.0 mode, 10-mV DAC - 0x24
IMVP8 mode, 5-mV DAC - 0x25
VR13.0 mode, 5-mV DAC - 0x27

Signed-off-by: Vadim Pasternak <vadimp@mellanox.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>