patman: Fix up checkpatch parsing to deal with 'CHECK' lines

checkpatch has a new type of warning, a 'CHECK'. At present patman fails
with these, which makes it less than useful.

Add support for checks, making it backwards compatible with the old
checkpatch.

At the same time, clean up formatting of the CheckPatches() output,
fix erroneous "internal error" if multiple patches have warnings and
be more robust to new types of problems.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Doug Anderson <dianders@chromium.org>