ANDROID: Add defconfig for cuttlefish.

This file is based on x86_64_defconfig, merged with the base and
recommended configs from configs.git, with the virtio drivers enabled
and some spurious kernel features turned off.

(This version differs from the 4.9 and 4.14 versions because it uses the
 deprecated ANDROID_LOW_MEMORY_KILLER feature instead of MEMCG.)

Change-Id: I61bde941e8cfef2dd83cb4ff040f7380922cc44e
Signed-off-by: Alistair Strachan <astrachan@google.com>