ANDROID: Add dtdiff target for testing

Test: m dtdiff && dtdiff a.dtb b.dtb
Change-Id: I38790cd62e1e6e7b94cd489a6f94f3ba185f27f6
diff --git a/Android.bp b/Android.bp
index 2d121ec..ee55bfa 100644
--- a/Android.bp
+++ b/Android.bp
@@ -119,6 +119,11 @@
     ],
 }
 
+sh_binary_host {
+    name: "dtdiff",
+    src: "dtdiff",
+}
+
 genrule {
     name: "dtc_version_gen.h",
     out: ["version_gen.h"],