HID: wacom: support named keys on older devices

Some Wacom devices have keys with predefined meanings. However, when
support was originally added for these devices, the codes for these
keys were not available yet. These keys were thus reported with
the numbered KEY_PROG* range.

Some missing key codes were added with commit 4eb220cb

 ("HID:
wacom: generic: add 3 tablet touch keys") and we are now able to
report the proper key codes. We continue to report the original
KEY_PROG codes so as not to break any unknown applications that
may depend on them.

Also, to support the touch key, track its state in the pad report.

Signed-off-by: Aaron Armstrong Skomra <aaron.skomra@wacom.com>
Link: https://gitlab.freedesktop.org/libinput/libinput/merge_requests/155
Link: https://github.com/linuxwacom/xf86-input-wacom/pull/46


Reviewed-by: Ping Cheng <ping.cheng@wacom.com>
Reviewed-by: Jason Gerecke <jason.gerecke@wacom.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>