it87: Add support for the IT8718F

The IT8718F is a Super-I/O chip with integrated hardware monitoring
functions. It is very similar to the IT8716F, so adding support to the
it87 driver was pretty straightforward. The most significant difference
is that the IT8718F has up to 8 VID pins, instead of 6 for the older
chips.

For the IT8718F, the VID value can only be read from Super-I/O space.

Userspace support is already in lm_sensors SVN (to be soon released
as 2.10.1.)
Signed-off-by: NJean Delvare <khali@linux-fr.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>