HID: multitouch: fix Asus ExpertBook P2 P2451FA trackpoint

The HID descriptor of this device contains two mouse collections, one
for mouse emulation and the other for the trackpoint.

Both collections get merged and, because the first one defines X and Y,
the movemenent events reported by the trackpoint collection are
ignored.

Set the MT_CLS_WIN_8_FORCE_MULTI_INPUT class for this device to be able
to receive its reports.

This fix is similar to/based on commit 40d5bb87 ("HID: multitouch:
enable multi-input as a quirk for some devices").

Link: https://gitlab.freedesktop.org/libinput/libinput/-/issues/825


Reported-by: Akito <the@akito.ooo>
Tested-by: Akito <the@akito.ooo>
Signed-off-by: José Expósito <jose.exposito89@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>