HID: multitouch: add handling for pen in dual-sensors device

Dual sensors devices reports pen and touch on two different reports.
Using the quirk HID_QUIRK_MULTI_INPUT allows us to create a new input
device to forward pen events.

The quirk HID_QUIRK_NO_EMPTY_INPUT avoids the creation of input devices
for the not used mouse emulation present on Win7 certified devices.

Since hid-multitouch sets the quirk HID_QUIRK_NO_INPUT_SYNC, we need
to manually send SYN events for pen report too.

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