of: dynamic: add lifecycle docbook info to node creation functions

The existing docbook comments for the functions related to creating
a devicetree node do not explain the reference count of a newly
created node, how decrementing the reference count to zero will
free the associated memory, and the caller's responsibility to
call of_node_put() on the node.  Explain what happens when the
reference count is decremented to zero.

Signed-off-by: Frank Rowand <frowand.list@gmail.com>
Link: https://lore.kernel.org/r/20230213185702.395776-8-frowand.list@gmail.com


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