[coreboot] patch: more path support

[ron minnich]

let's get the dts right before I submit any more code. I want us all
to be happy with this.

Let's start with this dts:
/{
        mainboard-vendor = "Emulation";
        mainboard-name = "QEMU x86";
        enabled;
        constructor = "qemuvga_constructors";
        cpus {};
        domain at 0 {
                /config/("northbridge/intel/i440bxemulation/dts");
                bus at 0 {
                        pci at 0,0 {
                        };
                        pci at 1,0 {
                                /config/("southbridge/intel/i82371eb/dts");
                        };
                };
        };
};


how do you want it to look? Recall, however, that the x at y syntax is
well understood by various OFW tools; changes to this should be
carefully done.

Thanks for comments and patience!

ron