pruss: Make sure it works when no child nodes are present

Pruss shouldn't fail when no child nodes are present.
PRU remote proc wip
bone: capemgr: Introduce simple resource tracking

Now each cape can declare an exclusive-use property which is
a string list of every resource it requires.
Attempting to load a cape that uses the same resource will fail.
capes: Add resources to capes.

Start adding the resource list of each cape.