HID: wacom: do not send pen events before touch is up/forced out

HID: wacom: do not send pen events before touch is up/forced out

If pen comes in proximity while touch is down, we force touch up
before sending pen events. Otherwise, there can be unfinished
touch events compete with pen events. This idea has been fully
implemented for Tablet PCs. But other tablets that support both
pen and touch are not fully considered.

Signed-off-by: Ping Cheng <pingc@wacom.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>