checkpatch.pl: check for the FSF mailing address

This check code is imported from Linux v3.17 checkpatch.pl.

Change-Id: If39d834ee9b6131bccc92de38fd7c108650bd2f1
Signed-off-by: Antony Pavlov <antonynpavlov@gmail.com>
Reviewed-on: http://openocd.zylin.com/2341
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>
Tested-by: Spencer Oliver <spen@spen-soft.co.uk>