HID: wacom - Add default permission defines for sysfs attributes

RW : ug=rw,o=r
WO : ug=w

And enabled reading relavent sysfs attributes.

Signed-off-by: Paul A. Tessier <phernost@gmail.com>
Signed-Off-by: Ping Cheng <pingc@wacom.com>
Tested-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>