We want to get rid of the concept of loading an external device tree and instead
generate our own. However, to do this we need to also create a device tree
template programatically.

This patch adds a helper to create an empty device tree in memory.

Signed-off-by: Alexander Graf <agraf@suse.de>
Reviewed-by: Peter Crosthwaite <peter.crosthwaite@petalogix.com>