Merge "Default to a u-boot prebuilt when no bootloader or kernel is provided in VirtualMachineConfig" into main am: fd6a147872 am: bb0c149925

Original change: https://android-review.googlesource.com/c/platform/packages/modules/Virtualization/+/3127022

Change-Id: I9b0588fac295406caf4dc1e4cd2600247c98cd0c
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>