x11: make the tool lookup dependent on the hw id as well

x11: make the tool lookup dependent on the hw id as well

Tools on the same physical item have the same serial number, so the eraser
and the pen part of a single pen share that serial number. With the current
lookup code, we'll always return whichever tool comes first into proximity.

Change the code to use the hw id in addition to the serial number, this way we
can differ between two tools.