install: create_device_rootfs: install pmos-base-systemd first

Note: This patch makes some assumptions about what we decide for https://gitlab.com/postmarketOS/pmaports/-/merge_requests/5377, so let's not merge it until that MR is ready...

When building a systemd image, this patch installs pmos-base-systemd (and its dependencies) first before building the rest of the device chroot. This is a workaround for...

The pmos-base-systemd package provides distro-wide systemd presets for services, and when it's added to the install_packages list then there's no guarantee that apk will install it before service packages execute systemctl preset. In other words: preset may be run before the distro presets are actually installed, and crushing expectations. By making sure pmos-base-systemd is installed in the chroot first, we can provide some guarantee that presets will be there when services are installed a bit later.