Move relocation_packer from Android.mk to Android.bp

Change-Id: I3d24f8513fe3ca19900705d4861ab797464e0930
diff --git a/tools/Android.bp b/tools/Android.bp
new file mode 100644
index 0000000..b44c296
--- /dev/null
+++ b/tools/Android.bp
@@ -0,0 +1 @@
+subdirs = ["*"]