hwmon: (it87) Add support for fan4 and fan5

Add support for the IT8716F and IT8718F fan4 and fan5. The late
revisions of the IT8712F have these too but support is harder to add
and nobody asked for it yet, so I didn't include it.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Mark M. Hoffman <mhoffman@lightlink.com>