plat/qemu: Bump the maximum image size am: cebb969d97

Original change: https://android-review.googlesource.com/c/trusty/external/trusted-firmware-a/+/3114667

Change-Id: I1d1219919a981ad3a1a1cd5a5cfbc44bb6f9741e
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>