UPSTREAM: of: Refactor __of_node_alloc() into __of_node_dup()

Add a node argument to __of_node_alloc() and rename it to
__of_node_dup() so that it can also be used to duplicate a node with
its properties. This is important for the overlay code so that it can
create new nodes without using separate changeset items for every single
property.

At the same time rework the overlay code to use the new function and
drop the extra changeset items.

Signed-off-by: Grant Likely <grant.likely@linaro.org>
(cherry picked from commit e51795815ef1a7adc018cbaf05aac46e3d24eda8)
Bug: 109890997
Change-Id: I5b43c2883a93bf730306e9bb32da8de141b35015
Signed-off-by: John Stultz <john.stultz@linaro.org>