Run compsvc on CompOS boot

Bug: 186126809
Test: 1. follow microdroid/README.md except payload.img:
        $ adb shell 'cd /data/local/tmp/microdroid;    \
           /apex/com.android.virt/bin/mk_payload       \
           /apex/com.android.compos/etc/payload_config.json \
           payload.img'
	$ adb shell 'chmod go+r /data/local/tmp/microdroid/payload*'
      2. adb shell /apex/com.android.virt/bin/vm run \
           /data/local/tmp/microdroid/microdroid.json

Change-Id: I03cc937c0f82cbcc4fd1064ce2135619f22b4170
diff --git a/compos/apex/Android.bp b/compos/apex/Android.bp
index 7ced384..3a8f601 100644
--- a/compos/apex/Android.bp
+++ b/compos/apex/Android.bp
@@ -40,4 +40,12 @@
         "compsvc_worker",
         "pvm_exec",
     ],
+
+    apps: [
+        "CompOSPayloadApp",
+    ],
+
+    prebuilts: [
+        "compos_payload_config",
+    ],
 }