build: set TARGET_SUPPORTS_64_BIT_APPS in 64-bit config

Set TARGET_SUPPORTS_32_BIT_APPS and TARGET_SUPPORTS_64_BIT_APPS,
TARGET_PREFERS_32_BIT_APPS is enough to get apps to build for
32-bit only, and leaving TARGET_SUPPORTS_64_BIT_APPS unset
confuses zygote64 because it finds an empty 64-bit ABI list.

Change-Id: Iadea7f2b42c216710b54aeac6011a4e30e0f2eaa