hwmon: (adm1031) Add sysfs files for temperature offsets

The ADM1030/ADM1031 chips have temperature offset registers, for both the
local and remote temperature sensors. Following the example set forth in
the LM90/ADM1032 driver, expose the offset registers to userspace.

Signed-off-by: Ira W. Snyder <iws@ovro.caltech.edu>
Signed-off-by: Jean Delvare <khali@linux-fr.org>