[PNPACPI] Ignore devices that have no resources

Ignore devices that don't have a _CRS method.
They are useless for the PNP layer as they don't provide any resources.

Cc: Adam Belay <ambx1@neo.rr.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Len Brown <len.brown@intel.com>