Add interface definition for binderized Keymaster HAL

Test: accepted by hidl-gen
Bug: 32020919,32962548
Change-Id: Ib0decb231527e944e6b673017b721ea4601b7b2a
diff --git a/keymaster/Android.bp b/keymaster/Android.bp
new file mode 100644
index 0000000..09b8cb2
--- /dev/null
+++ b/keymaster/Android.bp
@@ -0,0 +1,4 @@
+// This is an autogenerated file, do not edit.
+subdirs = [
+    "3.0",
+]