microdroid: userdata/payload as bootdevices

so that partitions in those disks are available via /dev/block/by-name
symlinks.

Bug: n/a
Test: MicrodroidHostTestCases
Change-Id: I2aaa88f05220f97b87b19fef3ffdaff3d4282e12
diff --git a/microdroid/Android.bp b/microdroid/Android.bp
index 47f3474..f2030d1 100644
--- a/microdroid/Android.bp
+++ b/microdroid/Android.bp
@@ -168,7 +168,9 @@
             kernel_prebuilt: ":kernel_prebuilts-5.10-x86_64",
             cmdline: microdroid_boot_cmdline +
                 "pci=noacpi " +
-                "androidboot.boot_devices=pci0000:00/0000:00:01.0",
+                "androidboot.boot_devices=pci0000:00/0000:00:01.0," + // os
+                "pci0000:00/0000:00:03.0," + // payload
+                "pci0000:00/0000:00:04.0", // userdata
         },
     },
     dtb_prebuilt: "dummy_dtb.img",