HID: wacom: add support of the Pen of the Bamboo Pad

Bamboo Pads are using the generic processing but their report descriptors
differ from the ISDv* line. The pen fields are marked with the .physical
as Digitizer_Pen, which makes also sense.

Add this field to the checks and enable for free Bamboo Pads.
Reported-by: NJosep Sanchez Ferreres <josep.sanchez.ferreres@est.fib.upc.edu>
Signed-off-by: NBenjamin Tissoires <benjamin.tissoires@redhat.com>
Reviewed-by: NJason Gerecke <killertofu@gmail.com>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>

drivers/hid/wacom_wac.h

@@ -74,6 +74,7 @@
 
 #define WACOM_PEN_FIELD(f)	(((f)->logical == HID_DG_STYLUS) || \
 				 ((f)->physical == HID_DG_STYLUS) || \
+				 ((f)->physical == HID_DG_PEN) || \
 				 ((f)->application == HID_DG_PEN))
 #define WACOM_FINGER_FIELD(f)	(((f)->logical == HID_DG_FINGER) || \
 				 ((f)->physical == HID_DG_FINGER) || \