HID: multitouch: add support for Nexio 42" panel

This device is the worst device I saw. It keeps TipSwitch and InRange
at 1 for fingers that are not touching the panel.
The solution is to rely on the field ContactCount, which is accurate
as the correct information are packed at the begining of the frame.

Unfortunately, CountactCount is most of the time at the end of the report.
The solution is to pick it when we have the whole report in raw_event.

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>