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.

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