hwmon: (it87) Manage device specific features with table

This simplifies the code, improves runtime performance, reduces
code size (about 280 bytes on x86_64), and makes it easier
to add support for new devices.

Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Jean Delvare <khali@linux-fr.org>