patman: Allow use outside of u-boot tree

To make it usable in git trees not providing a patch checker
implementation, add a command line option, allowing to suppress patch
check. While we are at it, sort debug options alphabetically.

Also, do not raise an exception if checkpatch.pl is not found - just
print an error message suggesting to use the new option, and return
nonzero status.

   . unit test passes:
    $ ./patman  -t
    <unittest.result.TestResult run=7 errors=0 failures=0>
   . successfully used patman in the autotest tree to generate a patch
     email (with --no-check option)
   . successfully used patman in the u-boot tree to generate a patch
     email
   . `patman --help' now shows command line options ordered
     alphabetically

Signed-off-by: Vadim Bendebury <vbendeb@chromium.org>
Acked-by: Doug Anderson <dianders@chromium.org>
Acked-by: Simon Glass <sjg@chromium.org>