Merge raspberry and master

[Anders Björklund]

Need to have proper "boards", so that we can have both qemu and raspberry in the same branch.

This is needed for building for multiple targets as well, such as raspberry0w (armv6) for instance.

Need to split things that can be shared (package), with things that cannot (rootfs-overlay)

Have amd64 and arm64 as the default targets. Find a better way to inherit defconfig files.