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/Android.bp b/compos/Android.bp
index fc0517f..1611b68 100644
--- a/compos/Android.bp
+++ b/compos/Android.bp
@@ -55,3 +55,10 @@
         "com.android.compos",
     ],
 }
+
+// TODO(b/190503456) Remove this when vm/virtualizationservice generates payload.img from vm_config
+prebuilt_etc {
+    name: "compos_payload_config",
+    src: "payload_config.json",
+    filename: "payload_config.json",
+}