pvmfw: Use the Android Prebuilt Drop tool

Instead of manually uploading pre-builts (no reliable way to document
their origin), use the Android Prebuilt Drop tool (go/android-prebuilt)
to allow future updates to pvmfw.img to be instead done through an
update of the build_id in its .asciipb file.

Bug: 199717422
Test: -
Change-Id: I4f58f46d0d9e1084160e656512406034f8d33170
diff --git a/.prebuilt_info/pvmfw.asciipb b/.prebuilt_info/pvmfw.asciipb
new file mode 100644
index 0000000..4199b2b
--- /dev/null
+++ b/.prebuilt_info/pvmfw.asciipb
@@ -0,0 +1,12 @@
+drops {
+  android_build_drop {
+    build_id: "8134799"
+    target: "u-boot_pvmfw"
+    source_file: "pvmfw.img"
+  }
+  dest_file: "pvmfw/pvmfw.img"
+  version: ""
+  version_group: ""
+  git_project: "platform/packages/modules/Virtualization"
+  git_branch: "master"
+}