Input: wacom - add serial number for Graphire4 and old Bamboo

With the removal of BTN_TOOL_FINGER for tablet buttons and
expresskeys, serial number is needed to distingush if the
events were from a regular tool (stylus, eraser, or mouse)
or the attribures (buttons, strips, or wheels) on the tablet
since there are overlapped events between the tools and the
tablet attributes.

Signed-off-by: Ping Cheng <pingc@wacom.com>
Reviewed-by: Chris Bagwell <chris@cnpbagwell.com>
Reviewed-by: Henrik Rydberg <rydberg@euromail.se>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>