libtrusty: Android.mk -> Android.bp

Test: links

Change-Id: Ic64361f98e9e51b62bfda8b2b1c3a00ae03f0a37
diff --git a/trusty/Android.bp b/trusty/Android.bp
new file mode 100644
index 0000000..1b2e2c7
--- /dev/null
+++ b/trusty/Android.bp
@@ -0,0 +1,3 @@
+subdirs = [
+    "libtrusty",
+]