arch specific dependencies are supported for apex

The apex module type now supports arch specific native dependencies.

apex {
    name: "myapex",
    arch: {
        arm64: {
	    native_shared_libraries: ["arm64_only_lib"],
	},
    },
}

Bug: 174639241
Test: m nothing
Change-Id: I3f00aa87c480d4127b27d33e9620c4336824e937