pvmfw: Zero all scratch memory before guest runs am: 68533613ff

Original change: https://googleplex-android-review.googlesource.com/c/platform/packages/modules/Virtualization/+/23107371

Change-Id: I6c0c73a31a1e6b3256521753e662e4a97768ece7
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>