Add support for the Texas Instruments INA219 and INA226 power monitors.
Signed-off-by: NLothar Felten <l-felten@ti.com>
[guenter.roeck@ericsson.com: formatting cleanup; check for smbus word data;
 select PGA=8 for INA219]
Signed-off-by: NGuenter Roeck <guenter.roeck@ericsson.com>