input_id: fix detection of devices with mouse buttons

Assign ID_INPUT_MOUSE property to devices with mouse buttons and no axis.

Libinput tries to use libwacom on devices with tablet-pad capability
which are detected by ID_INPUT_TABLET_PAD=1 property so assign pointer
class by setting ID_INPUT_MOUSE=1 to devices with mouse buttons and let
libwacom override the class for Wacom pads.