defconfig: enable hypervisor debug driver on 8994 debug config

Enable hypervisor debug driver to help catch illegal memory
access issues by ensuring the corresponding memory ranges are
unmapped from stage 2.

Change-Id: I0b5576c5854c377264e8973f7194dc835c9277b5
Signed-off-by: Pratik Patel <pratikp@codeaurora.org>