The commit log check tool is ported from DPDK project. As DPDK project
is BSD-3-Clause License, so keep the license exceptions in LICENSE.rst
file.
Add commit log check target in Makefile.

Signed-off-by: Lijian Zhang <Lijian.Zhang@arm.com>
Reviewed-by: Tianyu Li <Tianyu.Li@arm.com>

Change-Id: Id103f616d621ec0c6f3f0bb6b28614ab13d7634d