of: unittest: annotate warnings triggered by unittest

Some tests in the devicetree unittests result in printk messages
from the code being tested.  It can be difficult to determine
whether the messages are the result of unittest or are potentially
reporting bugs that should be fixed.  The most recent example of
a person asking whether to be concerned about these messages is [1].

Add annotations for all messages triggered by unittests, except
KERN_DEBUG messages.  (KERN_DEBUG is a special case due to the
possible interaction of CONFIG_DYNAMIC_DEBUG.)

The format of the annotations is expected to change when unittests
are converted to use the kunit infrastructure when the broader
testing community has an opportunity to discuss the implementation
of annotations of test triggered messages.

[1] https://lore.kernel.org/r/6021ac63-b5e0-ed3d-f964-7c6ef579cd68@huawei.comSigned-off-by: Frank Rowand <frank.rowand@sony.com>
Signed-off-by: Rob Herring <robh@kernel.org>