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 4.4 version because it uses the does
 not set CONFIG_PHYSICAL_START which breaks `qemu -dtb'. Also,
 virtio-gpu is not enabled because it was not present in 3.18.)

Bug: 70214720
Change-Id: Ib877decd4e048ae8a48c1ed72f3029ad39a747a6
Signed-off-by: Alistair Strachan <astrachan@google.com>