asus-wmi: move generic code to asus-wmi

New Asus notebooks are using a WMI device similar to
the one used in Eee PCs. Since we don't want to load
a module named eeepc-laptop on Asus Notebooks, start by
copying all the code to asus-wmi.c.

Signed-off-by: Corentin Chary <corentincj@iksaif.net>
Signed-off-by: Matthew Garrett <mjg@redhat.com>