Use dynamic partition size am: b416ba5dc4

Original change: https://android-review.googlesource.com/c/platform/system/tools/mkbootimg/+/3482251

Change-Id: Ia92258ee6a43666b6a2247d03b8d9dd9f98a2d15
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>