HID: hid-ntrig: multitouch cleanup and fix

This cleans up the identification of multitouch groups and enables
the end of group sync.

Taps are now explicitly handled to adjust for the changes in the
event stream in multitouch mode.  Added triple and quad tap for the
benefit of tools that recognize different tap types but do not have
full multi touch support.

This cleans up the behavior particularly for the latest firmware, which
didn't work particularly well with the older version of the driver.

In this form, when multitouch is active, both mt and st events will come out of
the "N-Trig MultiTouch" device.  And when its not st events will come out of
"N-Trig Touchscreen".

Signed-off-by: Rafi Rubin <rafi@seas.upenn.edu>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>