Input: wacom - support one finger touch the touchscreen way

There are two types of 1FGT devices supported in wacom_wac.c.
Changing them to follow the existing touchscreen format, i.e.,
only report BTN_TOUCH as a valid tool type.

Touch data will be ignored if pen is in proximity. This requires
a touch up event sent if touch was down when pen comes in. The
touch up event should be sent before any pen events are emitted.
Otherwise, two pointers would race for the cursor.

However, we can not send a touch up inside wacom_tpc_pen since
pen and touch are on different logical port. That is why we
have to check if touch is up before sending pen events.

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