When generating the list of files to check by checkpatch.pl, the list
generated by `git ls-files` is filtered by a regular expression with
grep. Due to a malformed regex, the dot of `.md` was considered a
wildcard instead of a dot. This patch fixes this so that it matches
only dots, thus allowing the two following files to be checked:

* tools/cert_create/include/cmd_opt.h
* tools/cert_create/src/cmd_opt.c

Also extended the list of library directories to check by checkpatch
to exclude any folder starting with libfdt.

Change-Id: Ie7bf18efe4df29e364e5d67ba1118515304ed9a4
Signed-off-by: Antonio Nino Diaz <antonio.ninodiaz@arm.com>