builders/uimage: support aligning the FIT

This is necessary when writing to a MTD partition with a certain erasesize.

modules/hardware.nix

@@ -67,6 +67,7 @@ in {
       };
       loadAddress = mkOption { type = types.ints.unsigned; default = null; };
       entryPoint = mkOption { type = types.ints.unsigned; };
+      alignment = mkOption { type = types.ints.unsigned; default = null; description = "Alignment passed to `mkimage` for FIT"; };
       radios = mkOption {
         description = ''
           Kernel modules (from mac80211 package) required for the

modules/outputs.nix

@@ -111,7 +111,7 @@ in
       };
       uimage = liminix.builders.uimage {
         commandLine = concatStringsSep " " config.boot.commandLine;
-        inherit (config.hardware) loadAddress entryPoint;
+        inherit (config.hardware) loadAddress entryPoint alignment;
         inherit (config.boot) imageFormat;
         inherit (o) kernel dtb;
       };

pkgs/kernel/uimage.nix

@@ -20,6 +20,7 @@ in {
 , extraName ? ""                # e.g. socFamily
 , loadAddress
 , imageFormat
+, alignment ? null
 , dtb ? null
 } : stdenv.mkDerivation {
   name = "kernel.image";
@@ -70,7 +71,7 @@ in {
         };
     };
     _VARS
-    mkimage -f mkimage.its kernel.uimage
+    mkimage -f mkimage.its ${lib.optionalString (alignment != null) "-B 0x${lib.toHexString alignment}"} kernel.uimage
     mkimage -l kernel.uimage
   '';