of: find_node_by_full_name rewrite to compare each level

find_node_by_full_name() does the same thing as of_find_node_by_path(),
but takes no locks and doesn't work on aliases. Refactor
of_find_node_opts_by_path() into __of_find_node_by_full_path() and
replace find_node_by_full_name() with it.

Signed-off-by: Rob Herring <robh@kernel.org>