mkosi: Make system dependencies conditional on format

If the none format is specified, we don't use the extra trees at all
so let's make the dependencies on the subimages conditional on Format=
not being set to "none".

This speeds up builds when using Format=none.

mkosi.images/system/mkosi.conf

@@ -1,14 +1,7 @@
 # SPDX-License-Identifier: LGPL-2.1-or-later
 
 [Config]
-Dependencies=
-        exitrd
-        minimal-base
-        minimal-0
-        minimal-1
-
-InitrdInclude=
-        initrd/
+InitrdInclude=initrd/
 
 [Output]
 @Format=directory
@@ -18,14 +11,6 @@ RepartDirectories=mkosi.repart
 Autologin=yes
 ExtraTrees=
         %D/mkosi.crt:/usr/lib/verity.d/mkosi.crt # sysext verification key
-        %O/minimal-0.root-%a.raw:/usr/share/minimal_0.raw
-        %O/minimal-0.root-%a-verity.raw:/usr/share/minimal_0.verity
-        %O/minimal-0.root-%a-verity-sig.raw:/usr/share/minimal_0.verity.sig
-        %O/minimal-1.root-%a.raw:/usr/share/minimal_1.raw
-        %O/minimal-1.root-%a-verity.raw:/usr/share/minimal_1.verity
-        %O/minimal-1.root-%a-verity-sig.raw:/usr/share/minimal_1.verity.sig
-        %O/minimal-base:/usr/share/TEST-13-NSPAWN-container-template
-        %O/exitrd:/exitrd
         leak-sanitizer-suppressions:/usr/lib/systemd/leak-sanitizer-suppressions
 
 PostInstallationScripts=mkosi.sanitizers.chroot

mkosi.images/system/mkosi.conf.d/20-images.conf

@@ -0,0 +1,21 @@
+# SPDX-License-Identifier: LGPL-2.1-or-later
+
+[Match]
+Format=!none
+
+[Config]
+Dependencies=
+        exitrd
+        minimal-base
+        minimal-0
+        minimal-1
+
+ExtraTrees=
+        %O/minimal-0.root-%a.raw:/usr/share/minimal_0.raw
+        %O/minimal-0.root-%a-verity.raw:/usr/share/minimal_0.verity
+        %O/minimal-0.root-%a-verity-sig.raw:/usr/share/minimal_0.verity.sig
+        %O/minimal-1.root-%a.raw:/usr/share/minimal_1.raw
+        %O/minimal-1.root-%a-verity.raw:/usr/share/minimal_1.verity
+        %O/minimal-1.root-%a-verity-sig.raw:/usr/share/minimal_1.verity.sig
+        %O/minimal-base:/usr/share/TEST-13-NSPAWN-container-template
+        %O/exitrd:/exitrd