libpdbg: Use real targets instead of system targets
libpdbg: Use real targets instead of system targets

The "real" fsi target is defined in the backend and is always the parent
of "real" pib target.  Use the appropriate api to search the backend
device tree instead of system device tree.

Signed-off-by: Amitay Isaacs <a505e7c038746dbeb3edcd8d146dbd515432801f@ozlabs.org>

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