Revert "final removal of CONFIG_EXPERIMENTAL"

Since we build with wireless-3.8 which still has some dependencies on
CONFIG_EXPERIMENTAL, we need to remove this.

BUG=None
TEST=None

This reverts commit 3d374d09f16f64ab4d71704cbe621514d36cd0b1.

Change-Id: Ie0e260fe3e67839ee253a19ae794156d1173750d
Signed-off-by: Derek Basehore <dbasehore@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/181550
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Benson Leung <bleung@chromium.org>