Add option to use GKI kernel for microdroid

With either payload config's osName field or config file's os field, a
GKI kernel can be used to run microdroid instead of microdroid kernel.
This also adds a new option --gki to the VM tool.

Bug: 305118971
Test: run VM with --gki
Change-Id: I87eb445c84bd208df549712aea7f55ab148c7f8a
diff --git a/microdroid/microdroid_gki.json b/microdroid/microdroid_gki.json
new file mode 100644
index 0000000..d7ba53e
--- /dev/null
+++ b/microdroid/microdroid_gki.json
@@ -0,0 +1,20 @@
+{
+  "kernel": "/apex/com.android.virt/etc/fs/microdroid_gki_kernel",
+  "disks": [
+    {
+      "partitions": [
+        {
+          "label": "vbmeta_a",
+          "path": "/apex/com.android.virt/etc/fs/microdroid_vbmeta.img"
+        },
+        {
+          "label": "super",
+          "path": "/apex/com.android.virt/etc/fs/microdroid_super.img"
+        }
+      ],
+      "writable": false
+    }
+  ],
+  "memory_mib": 256,
+  "platform_version": "~1.0"
+}