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/fstab.microdroid b/microdroid/fstab.microdroid
index 9478c7c..da000b9 100644
--- a/microdroid/fstab.microdroid
+++ b/microdroid/fstab.microdroid
@@ -1 +1,7 @@
 system /system ext4 noatime,ro,errors=panic wait,slotselect,avb=vbmeta,first_stage_mount,logical
+# This is a temporary solution to unblock other devs that depend on /vendor partition in Microdroid
+# The /vendor partition will only be mounted if the kernel cmdline contains
+# androidboot.microdroid.mount_vendor=1.
+# TODO(b/285855430): this should probably be defined in the DT
+# TODO(b/285855436): should be mounted on top of dm-verity device
+/dev/block/by-name/microdroid-vendor /vendor ext4 noatime,ro,errors=panic wait,first_stage_mount