HID: magicmouse: report last touch up

The evdev multitouch protocol requires that a last MT sync event must be
sent after all touches are up. This change adds the last MT sync event
to the hid-magicmouse driver.

Also, don't send events when a touch leaves.

Signed-off-by: Chase Douglas <chase.douglas@canonical.com>
Acked-by: Michael Poole <mdpoole@troilus.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>