hwmon: (it87) Introduce configuration field for chip suffix

ITE chips may have 'E', 'F', or both 'E' and 'F' suffixes.
Introduce suffic configuration to the it87_devices structure
to simplify adding new chips.

Reviewed-by: Jean Delvare <jdelvare@suse.de>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>