ath25: fix duplicate LZMA compression

The conversion to the new image building code accidentally caused the kernel
image to get compressed twice, leading to boot failures when kernel and rootfs
are flashed separately.

The sysupgrade images have been unaffected by this. Also restore the elf
kernel build artifact while we're at it.

Signed-off-by: Jo-Philipp Wich <jo@mein.io>

target/linux/ath25/image/Makefile

@@ -42,19 +42,30 @@ define Build/lzma-kernel
 	dd if=$@.l7 of=$@ bs=65536 conv=sync
 endef
 
+define Build/copy-kernel
+	rm -f $@ $@.elf
+	cp $< $@
+	cp $< $@.elf
+endef
+
+define Build/elf-kernel
+	cp $(IMAGE_KERNEL).elf $@
+endef
+
 
 define Device/Default
   PROFILES = Default $$(DEVICE_NAME)
-  KERNEL := kernel-bin | lzma-kernel
+  KERNEL := copy-kernel | lzma-kernel
   IMAGES := sysupgrade.bin
   FILESYSTEMS := squashfs
 endef
 
 define Device/generic
   DEVICE_TITLE := Generic Images
-  IMAGES := kernel.lzma kernel.gz rootfs.bin sysupgrade.bin
-  IMAGE/kernel.gz := append-kernel | gzip-kernel
-  IMAGE/kernel.lzma := append-kernel | lzma-kernel
+  IMAGES := kernel.lzma kernel.elf kernel.gz rootfs.bin sysupgrade.bin
+  IMAGE/kernel.gz := elf-kernel | gzip-kernel
+  IMAGE/kernel.elf := elf-kernel
+  IMAGE/kernel.lzma := elf-kernel | lzma-kernel
   IMAGE/rootfs.bin := append-rootfs | pad-rootfs | pad-to 128k
   IMAGE/sysupgrade.bin := append-rootfs | pad-rootfs | pad-to 128k | combined-image
   IMAGE_NAME = $$(IMAGE_PREFIX)-$$(if $$(findstring kernel,$$(2)),,$$(1)-)$$(2)