wmi: Add support for module autoloading

WMI provides interface-specific GUIDs that are exported from modules as
modalises, but the core currently generates no events to trigger module
loading. This patch adds support for registering devices for each WMI GUID
and generating the appropriate uevent.

Based heavily on a patch by Carlos Corbacho (<carlos@strangeworlds.co.uk>).

Signed-off-by: Matthew Garrett <mjg@redhat.com>
Tested-by: Carlos Corbacho <carlos@strangeworlds.co.uk>
Acked-by: Carlos Corbacho <carlos@strangeworlds.co.uk>
Signed-off-by: Len Brown <len.brown@intel.com>