src/plat/kevin: allow to override atf and fit

This commit lifts `atf` and `fit` into the ownerboot scope where
they can be selectively overridden.

src/platform/kevin/default.nix

@@ -65,18 +65,20 @@ in {
     # https://github.com/SolidHal/servo-v2-breakout-board
     console-device = "ttyS2";
 
+    atf = final.nixpkgsOnBuildForHost.callPackage (import ./atf) {
+      buildArmTrustedFirmware = (final.nixpkgsOnBuildForHost.arm-trusted-firmware.override {
+        unfreeIncludeHDCPBlob = false;
+        openssl = null;    # not sure why they would link in openssl...
+      }).buildArmTrustedFirmware;
+    };
+
+    fit = final.nixpkgsOnBuildForBuild.callPackage (import ./fit) {
+      inherit (final) initramfs kernel;
+    };
+
     coreboot =
-      let atf = final.nixpkgsOnBuildForHost.callPackage (import ./atf) {
-            buildArmTrustedFirmware = (final.nixpkgsOnBuildForHost.arm-trusted-firmware.override {
-              unfreeIncludeHDCPBlob = false;
-              openssl = null;    # not sure why they would link in openssl...
-            }).buildArmTrustedFirmware;
-          };
-          fit = final.nixpkgsOnBuildForBuild.callPackage (import ./fit) {
-            inherit (final) initramfs kernel;
-          };
-      in (prev.coreboot.override {
-        payload = "${fit}/Image.fit";
+      (prev.coreboot.override {
+        payload = "${final.fit}/Image.fit";
         fmap = ./custom.fmap;
         config = with lib.kernel; {
           CBFS_PREFIX = lib.mkForce (freeform "prefix");
@@ -109,7 +111,7 @@ in {
           CONSOLE_CBMEM = lib.mkForce no;
           COLLECT_TIMESTAMPS = lib.mkForce no;
 
-          ARM64_BL31_EXTERNAL_FILE = lib.mkForce (freeform "${atf}/bl31.elf");
+          ARM64_BL31_EXTERNAL_FILE = lib.mkForce (freeform "${final.atf}/bl31.elf");
         };
         coreboot-toolchain = with final.coreboot-toolchain; [ aarch64 ];
         initramfs_image = null;  # it is part of the FIT image
@@ -120,11 +122,11 @@ in {
       }).overrideAttrs (a: {
         postConfigure = ''
           mkdir -p 3rdparty/arm-trusted-firmware/plat/rockchip/common/include/
-          ln -s ${atf}/plat_params.h 3rdparty/arm-trusted-firmware/plat/rockchip/common/include/
+          ln -s ${final.atf}/plat_params.h 3rdparty/arm-trusted-firmware/plat/rockchip/common/include/
           mkdir -p 3rdparty/arm-trusted-firmware/plat/rockchip/rk3399/include/shared/
-          ln -s ${atf}/bl31_param.h 3rdparty/arm-trusted-firmware/plat/rockchip/rk3399/include/shared/
+          ln -s ${final.atf}/bl31_param.h 3rdparty/arm-trusted-firmware/plat/rockchip/rk3399/include/shared/
           mkdir -p 3rdparty/arm-trusted-firmware
-          ln -s ${atf}/include 3rdparty/arm-trusted-firmware/include
+          ln -s ${final.atf}/include 3rdparty/arm-trusted-firmware/include
         '';
       });