hwmon: (asus_atk0110) Add debugfs interface

Expose the raw GGRP/GITM interface via debugfs. The hwmon interface is
reverse engineered and the driver tends to break on newer boards...
Using this interface it's possible to poke directly at the ACPI methods
without the need to recompile, reducing the guesswork and the round trips
needed to support a new revision of the interface.

Signed-off-by: Luca Tettamanti <kronos.it@gmail.com>
Signed-off-by: Jean Delvare <khali@linux-fr.org>