[coreboot] patch: allow dts names to end in .dts

[ron minnich]

If a dts name ends in .dts, e.g.
                                /config/("southbridge/nvidia/mcp55/ide.dts");
it will be used. The node label will have the .dts removed.

Attached. Tested on builds and it looks fine. Now you can all stop
telling me to do this :-)

ron