samples: move misc-devices/mei example code from Documentation

Move misc-devices/mei examples to samples/mei and remove it from
Documentation Makefile. Delete misc-devices/Makefile.

Create a new Makefile to build samples/mei. It can be built from top
level directory or from mei directory:

Run make -C samples/mei or cd samples/mei; make

Acked-by: Jonathan Corbet <corbet@lwn.net>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>