hwmon: (ina238) Add support for INA700

hwmon: (ina238) Add support for INA700

INA700 is register compatible to INA780 but has different current, power,
and energy LSB values.

While the chip does not directly report the shunt voltage, report
it anyway by calculating its value from the current register.

Reviewed-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
Tested-by: Chris Packham <chris.packham@alliedtelesis.co.nz> # INA780
Cc: Christian Kahr <christian.kahr@sie.at>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>