radiobert: try to make it bootable again

actually try this on a day with nice weather

hosts/radiobert/default.nix

@@ -26,14 +26,13 @@
 
   boot = {
     loader = {
+      # generates entry for u-boot
+      generic-extlinux-compatible.enable = true;
       grub.enable = false;
       raspberryPi = {
-        enable = true;
+        # don't use rpi bootloader shit
+        enable = false;
         version = 4;
-        # TODO: this machine actually has u-boot setup but that's no
-        # longer working with nixos-22.05. DO NOT REBOOT! :-)
-        # https://github.com/NixOS/nixpkgs/pull/112677
-        # uboot.enable = true;
         firmwareConfig = ''
           gpu_mem=192
           dtparam=audio=on