aosp_arm64: add the android-4.19-stable Image.gz prebuilt am: b068fe1bc8 am: 7e0079fe88 am: 2f98c4cfe4

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

Change-Id: I6c83d8ff9af1d4435d068cbb59c306c38da2d1ff