of: unittest: add program to process EXPECT messages

If unittest detects a problem it will print a warning or error message
to the console.  Unittest also triggers warning and error messages from
other kernel code as a result of intentionally bad unittest data.  This
has led to confusion as to whether the triggered messages are an
expected result of a test or whether there is a real problem that is
independent of unittest.

EXPECT messages were added to unittest to report each triggered message
that is expected, resulting in verbose console output.

scripts/dtc/of_unittest is a new program that processes the EXPECT
messages to determine whether the triggered messages occurred and
also removes the excess verbosity of the EXPECT messages.  More
information is available from 'scripts/dtc/of_unittest_expect --help'.

Signed-off-by: Frank Rowand <frank.rowand@sony.com>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220201181413.2719955-1-frowand.list@gmail.com