Update validation-layer.jd for NDK-R12:    use packed layer binaries    punt building layers to Khronos github repo am: c1755d345d am: 999b7afac8 am: 3c76d062ae
am: a17a07ad8e

Change-Id: I023b5ae196ddd5b491c1a7c89d21e465ef3de70e