HID: asus: Parameterize the touchpad code

Instead of having hardcoded (#define-d) values use a struct describing
the various touchpad parameters. This is a preparation patch for
improving the T100TA touchpad support as well as for adding T100CHI
touchpad support.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>