HID: hid-multitouch: forward MSC_TIMESTAMP

Computes and forwards the device timestamp according to the specification.

Many devices use a 16-bit timestamp field, with a resolution of 100us,
therefore rolling around very frequently (every 6.5 seconds). To make sure
there is no ambiguity, the timestamp reported to the input stack reset to
0 whenever the time between 2 received events is greater than
MAX_TIMESTAMP_INTERVAL (1 second).

Signed-off-by: Nicolas Boichat <drinkcat@chromium.org>
Acked-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>