Fix ndk and aml arch order

Some codes assume that the first arch is the primary arch. But ndk/aml
arch order have been [arm, arm64, x86, x86_64]. This fixes the order to
workaround possible breakage while building ndk.

Bug: 187196593
Test: OUT_DIR=out build/soong/scripts/build-ndk-prebuilts.sh
Change-Id: I33164a7e7c64a23f2cc1860acb24a2584f4dffad