turny: fix SPI/GPIO config for newer kernels

- Add complete config.txt settings with u-boot boot lines + spi=on
- Override sdImage.populateFirmwareCommands to use configtxt module output
- Mount firmware partition and add activation script to sync config.txt
- Load spi_bcm2835 and bcm2835_gpiomem kernel modules
- Add udev rule for gpiomem subsystem (not just gpio)
- Relax ProtectKernelTunables so service can access GPIO
- Update turny flake input to rppal-based CS pin fix

hosts/freun-dev/configuration.nix

@@ -20,6 +20,8 @@ in
         "flakes"
       ];
       auto-optimise-store = true;
+      min-free = 5 * 1024 * 1024 * 1024;
+      max-free = 10 * 1024 * 1024 * 1024;
     };
     gc = {
       automatic = true;
@@ -28,6 +30,8 @@ in
     };
   };
 
+  services.journald.extraConfig = "SystemMaxUse=500M";
+
   boot.loader.systemd-boot.enable = true;
   boot.loader.efi.canTouchEfiVariables = true;
   boot.binfmt.emulatedSystems = [ "x86_64-linux" ];
@@ -164,6 +168,8 @@ in
     "builder"
   ];
 
+  modules.tempBuildStorage.enable = true;
+
   # List packages installed in system profile. To search, run:
   # $ nix search wget
   environment.systemPackages = with pkgs; [