hwmon: (pc87427) Add temperature monitoring support

Add support for the 6 temperature monitoring channels of the PC87427.
Note that the sensors resolution can vary, and I couldn't find a way
to figure it out, so we might have to compensate in user-space.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Acked-by: Guenter Roeck <guenter.roeck@ericsson.com>