cns3xxx: fix initramfs build

Signed-off-by: Felix Fietkau <nbd@openwrt.org>

Backport of r41915

git-svn-id: svn://svn.openwrt.org/openwrt/branches/barrier_breaker@41919 3c298f89-4303-0410-b956-a3cf2f4a3e73

target/linux/cns3xxx/image/Makefile

@@ -25,6 +25,10 @@ define BuildFirmware/Generic
 		$(BIN_DIR)/$(IMG_PREFIX)-$(patsubst jffs2-%,jffs2,$(patsubst squashfs-%,squashfs,$(1)))-sysupgrade.bin
 endef
 
+define Image/BuildKernel/Initramfs
+	mkimage -A arm -O linux -T kernel -C none -a 0x20008000 -e 0x20008000 -n 'OpenWrt Linux-$(LINUX_VERSION)' -d $(KDIR)/zImage-initramfs $(BIN_DIR)/$(IMG_PREFIX)-initramfs-uImage
+endef
+
 define Image/Build
 	$(call Image/Build/$(1),$(1))
 	$(call BuildFirmware/Generic,$(1))