HID: asus: ignore declared dummy usages

Keyboards handled by hid-asus declare special key functions
using a vendor-specific page, however, alongside legitimate
key functions, dummy usages with seemingly arbitrary values
are also declared and can lead to keyboards being detected
as pointer devices by some software (such as X.org).

In addition, for the I2C keyboard volume controls are
separately declared in a Consumer Usage page, with the same
dummy usage problem.

The fix in 1989dada ("HID: input: ignore System Control
application usages if not System Controls") does not mitigate
the problem described above, therefore dummy usages need to
be ignored in the driver itself.

This fix properly ignores dummy usages and introduces a quirk
for custom handling of the Consumer Usages on the I2C keyboard.

Signed-off-by: Matjaz Hegedic <matjaz.hegedic@gmail.com>
Reviewed-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>