Howto use the configfs overlay interface.

A device-tree configfs entry is created in /config/device-tree/overlays
and and it is manipulated using standard file system I/O.
Note that this is a debug level interface, for use by developers and
not necessarily something accessed by normal users due to the
security implications of having direct access to the kernel's device tree.

* To create an overlay you mkdir the directory:

	# mkdir /config/device-tree/overlays/foo

* Either you echo the overlay firmware file to the path property file.

	# echo foo.dtbo >/config/device-tree/overlays/foo/path

* Or you cat the contents of the overlay to the dtbo file

	# cat foo.dtbo >/config/device-tree/overlays/foo/dtbo

The overlay file will be applied, and devices will be created/destroyed
as required.

To remove it simply rmdir the directory.

	# rmdir /config/device-tree/overlays/foo

The rationalle of the dual interface (firmware & direct copy) is that each is
better suited to different use patterns. The firmware interface is what's
intended to be used by hardware managers in the kernel, while the copy interface
make sense for developers (since it avoids problems with namespaces).