Unlike EMR tools which encode type information in their tool ID, tools
for AES sensors are all "generic pens". It is inappropriate to make use
of the wacom_intuos_get_tool_type function when dealing with these kinds
of devices. Instead, we should only ever report BTN_TOOL_PEN or
BTN_TOOL_RUBBER, as depending on the state of the Eraser and Invert
bits.