HID: multitouch: Enable multi-input for Synaptics pointstick/touchpad device

Pointstick and its left/right buttons on HP EliteBook 850 G7 need
multi-input quirk to work correctly.

Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>