HID: wacom: generic: Add support for vendor-defined "Distance" usage

The vendor-defined 0xFF0D01032 ("Distance") usage is nearly equivalent to
HID_GD_Z, except that the axis direction is inverted. Unlike HID_GD_Z which
increases in value as the pen-to-surface distance is decreased, this usage
decreases. Treat this usage as a special case to ensure we don't invert the
scale to be ABS_DISTANCE compatible like we do for HID_GD_Z.

Signed-off-by: Jason Gerecke <jason.gerecke@wacom.com>
Reviewed-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>