hwmon: (pmbus/mp2975) Simplify VOUT code

hwmon: (pmbus/mp2975) Simplify VOUT code

In order to upstream MP2973/MP2971 simplify the code by removing support
for various VOUT formats. The MP2973 and MP2971 supports all PMBUS
supported formats for VOUT, while the MP2975 only support DIRECT and
VID for VOUT.

In DIRECT mode all chips report the voltage in 1mV/LSB.

Configure the chip to use DIRECT format for VOUT and drop the code
conversion code for other formats. The to be added chips MP2973/MP2971
will be configured to also report VOUT in DIRECT format.

The maximum voltage that can be reported in DIRECT format is 32768mV.
This is sufficient as the maximum output voltage for VR12/VR13 is
3040 mV.

Signed-off-by: Patrick Rudolph <patrick.rudolph@9elements.com>
Signed-off-by: Naresh Solanki <Naresh.Solanki@9elements.com>
Link: https://lore.kernel.org/r/20230714135124.2645339-4-Naresh.Solanki@9elements.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>