Propagate to Microdroid whether it should mount vendor partition

This is implemented by setting passing the
androidboot.microdroid.mount_vendor=1 to the cmdline of the Microdroid
kernel. The first_stage_init will parse the cmdline, and mount the
/vendor partition if it sees the value.

Bug: 285855433
Test: atest virtualizationmanager_device_test
Test: atest MicrodroidTestApp
Change-Id: I61b658a5c740488ff0591f00b2fee66b64b63c46
diff --git a/microdroid/Android.bp b/microdroid/Android.bp
index 5440695..2d3f084 100644
--- a/microdroid/Android.bp
+++ b/microdroid/Android.bp
@@ -23,6 +23,10 @@
     "apex",
     "linkerconfig",
     "second_stage_resources",
+
+    // Ideally we should only create the /vendor for Microdroid VMs that will mount /vendor, but
+    // for the time being we will just create it unconditionally.
+    "vendor",
 ]
 
 microdroid_symlinks = [