Input: synaptics - enable SMBUS on T480 thinkpad trackpad

Thinkpad t480 laptops had some touchpad features disabled, resulting in the
loss of pinch to activities in GNOME, on wayland, and other touch gestures
being slower. This patch adds the touchpad of the t480 to the smbus_pnp_ids
whitelist to enable the extra features. In my testing this does not break
suspend (on fedora, with wayland, and GNOME, using the rc-6 kernel), while
also fixing the feature on a T480.

Signed-off-by: Cole Rogers <colerogers@disroot.org>
Acked-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>