Fixes: <https://issues.guix.gnu.org/45584>. * gnu/system/image.scm (arm32-disk-image, arm64-disk-image): Turn into procedures, taking the root partition offset as argument. * gnu/system/images/novena.scm (novena-image-type): Adapt accordingly. * gnu/system/images/pine64.scm (pine64-image-type): Ditto. * gnu/system/images/pinebook-pro.scm (pinebook-pro-image-type): Use a 9MiB offset for the root partition.