mkosi: Switch to autologin via credentials

Let's use the newly added credentials to only enable autologin for
/dev/console (systemd-nspawn) and /dev/hvc0 (qemu) instead of enabling
autologin for every tty.

mkosi.conf

@@ -30,7 +30,6 @@ CacheDirectory=build/mkosi.cache
 
 [Content]
 BuildSourcesEphemeral=yes
-Autologin=yes
 
 ExtraTrees=
         mkosi.crt:/usr/lib/verity.d/mkosi.crt # sysext verification key
@@ -134,7 +133,12 @@ Packages=
         zstd
 
 [Host]
-Credentials=journal.storage=persistent
+Credentials=
+        journal.storage=persistent
+        tty.serial.hvc0.agetty.autologin=root
+        tty.serial.hvc0.login.noauth=yes
+        tty.console.agetty.autologin=root
+        tty.console.login.noauth=yes
 Incremental=yes
 RuntimeBuildSources=yes
 RuntimeScratch=no