[PATCH] powerpc: add for_each_node_by_foo helpers

Typical use for of_find_node_by_name and of_find_node_by_type is to
iterate over all nodes of a given type/name.  Add a helper macro to
do that (in spirit of the list_for_each* macros).

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Paul Mackerras <paulus@samba.org>