hwmon: (lm75) Add MAX31725/6 support

MAX31725/MAX31726 are local temperature sensors with +/- 0.5 degree
Celsius accuracy and 16-bit (0.00390625 degrees Celsius) resolution.
They have a register mapping and encoding compatible with the lm75
series drivers. Address scan and extended temperature range are
not supported by this patch.

Tested on real hardware and verified temperature readings are correct.

Signed-off-by: Kun Yi <kunyi@google.com>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>