hwmon: (adt7475) New documentation

New documentation for the adt7475 driver, based on the adt7473 driver
documentation. It is IMHO much more useful that the previous
documentation which was essentially redundant with sysfs-interface.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Cc: "Mark M. Hoffman" <mhoffman@lightlink.com>
Cc: Hans de Goede <hdegoede@redhat.com>
Cc: Jordan Crouse <jordan@cosmicpenguin.net>
Cc: "Darrick J. Wong" <djwong@us.ibm.com>