Input: surface3_spi - add surface pen support for Surface 3

This change creates a second input device which will handle input from
a Surface Pen. The Surface Pen supplies a different packet header than
touch events, so it is simple to handle one or the other.

This patch handles both the newer Surface Pen with one button, and the
older variant with a second button to switch to Eraser mode.

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>