You’d need to switch to another kernel which has a more complete config or get the kernel you’re using to be rebuilt with what you need.
I don’t know if the generic Ubuntu kernel is bootable on raspberry pi, if it is, it would include those bits (though would likely miss some rpi bits), otherwise, you’ll need to file a bug against the rpi kernel to ask for those bits to be added.
Running lxd.check-kernel should show what’s missing.