scripts: Add checkpatch.pl from the QEMU project

OSv's coding style is very similar to that of QEMU.  The script probably
needs some work with our C++ specific coding style but we have to start
somewhere...

Signed-off-by: Zhi Yong Wu <zwu.kernel@gmail.com>
Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>