Use debian-ports keyring for s390x.

Install unstable on s390x.

build/config/s390x.cfg

@@ -14,6 +14,12 @@ $(DEST)/parmfile.debian:
 
 DROP_LANG = '(?!en)'
 
+# The codename of the Debian release that should be installed by default.
+DEBIAN_RELEASE = unstable
+
+# s390x is currently hosted on debian-ports.org
+KEYRING = /usr/share/keyrings/debian-ports-archive-keyring.gpg
+
 arch_tree:
 	# Avoid loading partman-auto during anna
 	mkdir -p $(TREE)/var/cache/anna

debian/changelog

@@ -86,6 +86,8 @@ debian-installer (2011xxxx) UNRELEASED; urgency=low
   [ Aurelien Jarno ]
   * Add virtio udebs on s390/generic and s390/netboot.
   * Update kFreeBSD kernel to 8.2 (ABI 1).
+  * Use debian-ports keyring for s390x.
+  * Install unstable on s390x.
 
   [ Robert Millan ]
   * Enable netboot-gtk flavor on kfreebsd-amd64. Closes: #596596

debian/control

@@ -156,7 +156,7 @@ Build-Depends:
 #		Used as the CD-ROM's bootloader
 	xorriso [kfreebsd-i386 kfreebsd-amd64 hurd-i386],
 #               Used by grub-pc to create the CD-ROM images
-	debian-ports-archive-keyring [sh4 sparc64],
+	debian-ports-archive-keyring [s390x sh4 sparc64],
 #		Used for architectures hosted on debian-ports.org
 
 Package: debian-installer