fmap, payload: move to top-level scope

This commit moves the `fmap` and `payload` arguments to `coreboot`
into the top-level scope, so they can be provided without needing to
override the `coreboot` expression.

src/platform/am1i/default.nix

@@ -18,15 +18,12 @@
       });
 
     console-device = "ttyS1";
-
-    image = prev.image.override {
-      payload = "${final.kernel}/bzImage";
-    };
+    payload = "${final.kernel}/bzImage";
+    fmap = ./custom.fmap;
 
     coreboot = (prev.coreboot.override {
       iasl = final.iasl_20180531;
       coreboot-toolchain = with final.coreboot-toolchain; [ x64 i386 ];
-      fmap = ./custom.fmap;
       config = with lib.kernel; {
         CBFS_PREFIX = lib.mkForce (freeform "prefix");
 

src/platform/kevin/default.nix

@@ -76,14 +76,15 @@ in {
       inherit (final) initramfs kernel linux-command-line;
     };
 
+    payload = "${final.fit}/Image.fit";
+    fmap = ./custom.fmap;
+
     image = prev.image.override {
-      payload = "${final.fit}/Image.fit";
       initramfs = null;  # it is part of the FIT image
     };
 
     coreboot =
       (prev.coreboot.override {
-        fmap = ./custom.fmap;
         config = with lib.kernel; {
           CBFS_PREFIX = lib.mkForce (freeform "prefix");
 

src/platform/kgpe/default.nix

@@ -43,13 +43,11 @@
     # TODO: use a NixOS-style structuredConfig for this.
     cmos-default = null;
 
-    image = prev.image.override {
-      payload = "${final.kernel}/bzImage";
-    };
+    payload = "${final.kernel}/bzImage";
+    fmap = ./custom.fmap;
 
     coreboot = (prev.coreboot.override {
       iasl = final.iasl_20180531;
-      fmap = ./custom.fmap;
       config = with lib.kernel; {
         CBFS_PREFIX = lib.mkForce (freeform "prefix");