hwmon: (ina2xx) Add support for INA260

hwmon: (ina2xx) Add support for INA260

INA260 is similar to other chips of the series, except it has an internal
shunt resistor. The calibration register is therefore not present. Also,
the current register address was changed, though that does not matter for
the driver since the shunt voltage register (which is now the current
register) value is already used to read the current.

Cc: Loic Guegan <loic.guegan@mailbox.org>
Reviewed-by: Tzung-Bi Shih <tzungbi@kernel.org>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>