Add userdata partition to microdroid

Many programs need /data (especially /data/local/tmp) to properly work.
This change adds a basic unencrypted ext4 userdata partition to
microdroid. Eventually microdroid will support userdata encryption so
only VM can access /data.

Bug: 185767624
Test: atest MicrodroidHostTestCases
Test: log in to microdroid and test writing to /data
Change-Id: I115a8083ad6741fea9dedd61eca7194b1b5e5712
diff --git a/apex/Android.bp b/apex/Android.bp
index 8af22ff..91df00c 100644
--- a/apex/Android.bp
+++ b/apex/Android.bp
@@ -56,6 +56,7 @@
         "com.android.virt.init.rc",
         "microdroid_cdisk.json",
         "microdroid_cdisk_env.json",
+        "microdroid_cdisk_userdata.json",
         "microdroid_payload.json",
         "microdroid_uboot_env",
         "microdroid_bootloader",