Installation with heimdall-isorec method broken after https://gitlab.com/postmarketOS/boot-deploy/-/merge_requests/50

Hi, after !50 (merged) vmlinuz-dtb is no longer installed. This breaks the heimdall-isorec installation method, as that method uses that file. Only samsung-{i9100,i9100g,kiran} use this method at the moment.

I am not sure whether it would be best to fix this in boot-deploy or pmbootstrap, but I guess we can cat vmlinuz and the dtb somewhere in any case.