autotools: Deprecate the use of autotools

autotools: Deprecate the use of autotools

Since Meson will eventually be the only build system deprecate autotools
now. It can still be used by invoking configure with the flag
  --enable-autotools

NAKed-by: Ilia Mirkin <imirkin@alum.mit.edu>
Acked-by: Eric Engestrom <eric.engestrom@intel.com>
Acked-by: Kenneth Graunke <kenneth@whitecape.org>
Acked-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Acked-by: Rob Clark <robdclark@gmail.com>
Acked-by: Jason Ekstrand <jason@jlekstrand.net>
Acked-by: Marek Olšák <marek.olsak@amd.com>
Acked-by: Kristian H. Kristensen <hoegsberg@chromium.org>
Reviewed-by: Christian Gmeiner <christian.gmeiner@gmail.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Gert Wollny <gw.fossdev@gmail.com>