samples: move auxdisplay example code from Documentation

Move auxdisplay examples to samples and remove it from Documentation
Makefile. Create a new Makefile to build auxdisplay. It can be built
from top level directory or from auxdisplay directory:

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

Acked-by: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>