[media] DocBook: Use base64 for gif/png files

The patch utility doesn't work with non-binary files. This causes some
tools to break, like generating tarball targets and the scripts that
generate diff patches at http://www.kernel.org/pub/linux/kernel/v2.6/.

So, let's convert all binaries to ascii using base64, and add a
logic at Makefile to convert them back into binaries at runtime.

Reported-by: Randy Dunlap <randy.dunlap@oracle.com>
Reported-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Michal Marek <mmarek@suse.cz>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>