hwmon: (pmbus/lm25066) Support configurable sense resistor values

The appropriate mantissa values for the lm25066 family's direct-format
current and power readings are a function of the sense resistor
employed between the SENSE and VIN pins of the chip.  Instead of
assuming that resistance is always the same 1mOhm as used in the
datasheet, allow it to be configured via a device-tree property
("shunt-resistor-micro-ohms").

Signed-off-by: Zev Weiss <zev@bewilderbeest.net>
Link: https://lore.kernel.org/r/20210928092242.30036-8-zev@bewilderbeest.net


[groeck: Fixed checkpatch warnings]
Signed-off-by: Guenter Roeck <linux@roeck-us.net>