This patch adds a helper to search for a node's phandle by its path. This
is especially useful when the phandle is part of an array, not just a single
cell in which case qemu_devtree_setprop_phandle would be the easy choice.

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