libpdbg: Support paths including virtual nodes
libpdbg: Support paths including virtual nodes

With the presence of virtual nodes, some of the nodes can be reached
from the root using different paths:

  - using virtual nodes (which provide the system device tree view)
  - using the actual hwunits present in the backend (backend device tree)

Both device tree paths should result in the same target.

Signed-off-by: Amitay Isaacs <a505e7c038746dbeb3edcd8d146dbd515432801f@ozlabs.org>
Reviewed-by: Alistair Popple <e9adbcf81c8a36ccc628e09bc92d0e25e1c8e501@popple.id.au>

open-power/pdbg,open-power/pdbg,open-power/pdbg