Input: surface3_spi - Prepare to add support for Surface Pen

Surface Pens can be supported by handling a second report type. Prepare
for this change.

Signed-off-by: Stephen Just <stephenjust@gmail.com>
Reviewed-and-tested-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>