of: unittest: add node lifecycle tests

Add tests to exercise the actions that occur when the reference count
of devicetree nodes decrement to zero and beyond. Decrementing to
zero triggers freeing memory allocated for the node.

This commit will expose a pr_err() issue in of_node_release(), resulting
in some kernal warnings and stack traces.

When scripts/dtc/of_unittest_expect processes the console messages,
it will also report related problems for EXPECT messages due to the
pr_err() issue:
** missing EXPECT begin : 5

Signed-off-by: Frank Rowand <frowand.list@gmail.com>
Link: https://lore.kernel.org/r/20230213185702.395776-5-frowand.list@gmail.com
[robh: Fix !CONFIG_OF_DYNAMIC build]
Signed-off-by: Rob Herring <robh@kernel.org>