Makefile: add coccicheck target

Coccinelle is a program for static code analysis.
For details on Coccinelle see

	http://coccinelle.lip6.fr/



Add scripts/coccicheck copied from Linux kernel v4.14.

The coccicheck script executes the tests *.cocci in
directory scripts/coccinelle by calling spatch.

In Makefile add a coccicheck target. You can use it with

	make coccicheck MODE=<mode>

	where mode in patch, report, context, org.

Add a copy of Linux v4.14 file Documentation/dev-tools/coccinelle.rst
as doc/README.coccinelle.

Cc: Simon Glass <sjg@chromium.org>
Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>