HID: asus: Add T100CHI bluetooth keyboard dock touchpad support

Put the touchpad in native (absolute coordinate mode) and export it to
userspace as a touchpad rather then as a mouse.

Note this requires HID_QUIRK_MULTI_INPUT as the T100CHI keyboard dock
has all functionality on a single HID interface and userspace expects
touchpads to be on a separate input_dev. Without MULTI_INPUT userspace
will ignore the keyboard part of the keyboard/touchpad combo.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>