hwmon: LTC4261 Hardware monitoring driver

This driver adds support for Linear Technology LTC4261 I2C Negative
Voltage Hot Swap Controller.

Reviewed-by: Ira W. Snyder <iws@ovro.caltech.edu>
Reviewed-by: Tom Grennan <tom.grennan@ericsson.com>
Signed-off-by: Guenter Roeck <guenter.roeck@ericsson.com>