Add onPayloadReady callback

The guest VM can notify that its payload has finished initialization and
is ready to serve its own services, by onPayloadReady callback.

Bug: 195381416
Test: atest MicrodroidHostTestCases
Change-Id: I67fee655c410342452bc5ee990e36dfecb30b0cb
diff --git a/vm/src/run.rs b/vm/src/run.rs
index 825fdeb..4b656ae 100644
--- a/vm/src/run.rs
+++ b/vm/src/run.rs
@@ -189,6 +189,10 @@
         Ok(())
     }
 
+    fn onPayloadReady(&self, _cid: i32) -> BinderResult<()> {
+        Ok(())
+    }
+
     fn onPayloadFinished(&self, _cid: i32, _exit_code: i32) -> BinderResult<()> {
         Ok(())
     }