ANDROID: defconfig / build config for cuttlefish

Add defconfigs for x86_64 and arm64 for the cuttlefish virtual device
platform. This change also add the build.config files needed by the
kernel/build project.

Bug: 120439617
Test: make ARCH=x86_64 x86_64_cuttlefish_defconfig && make ARCH=x86_64
Test: make ARCH=arm64 cuttlefish_defconfig && make ARCH=arm64
Change-Id: I61bde941e8cfef2dd83cb4ff040f7380922cc44e
Signed-off-by: Alistair Strachan <astrachan@google.com>