Input: wacom - update Graphire4 and old Bamboo tablet buttons

Bamboo touch sets BTN_BACK, BTN_FORWARD, BTN_LEFT, and BTN_RIGHT
as the default button events for tablet buttons. Change Graphire4
and old Bamboo to the same settings.

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>