aosp_arm64: add the android-4.19-stable Image.gz prebuilt am: b068fe1bc8 am: 370fcd10b3

Original change: https://googleplex-android-review.googlesource.com/c/kernel/prebuilts/4.19/arm64/+/11885398

Change-Id: Id4aa479039857bcaffe62ab18340746a6ba32238