Add soong namespace for init scripts

* Not all devices can use those, so make them opt-in
* Stop conflicts with every qcom device tree that exists

Change-Id: I7930d9fca954904d1c0b6eed16e65a90b9440405
diff --git a/etc/Android.bp b/etc/Android.bp
index fbb2503..940391b 100644
--- a/etc/Android.bp
+++ b/etc/Android.bp
@@ -1,3 +1,6 @@
+soong_namespace {
+}
+
 prebuilt_etc {
     name: "init.qcom.usb.rc",
     src: "init.qcom.usb.rc",