brcm2708: fix image generation with imagebuilder

COPYING is not present in $(LINUX_DIR) on imagebuilder and prevents a
successful image creation.

Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>

target/linux/brcm2708/image/Makefile

@@ -12,6 +12,10 @@ include $(INCLUDE_DIR)/host.mk
 FAT32_BLOCK_SIZE=1024
 FAT32_BLOCKS=$(shell echo $$(($(CONFIG_BRCM2708_SD_BOOT_PARTSIZE)*1024*1024/$(FAT32_BLOCK_SIZE))))
 
+define Build/Compile
+	$(CP) $(LINUX_DIR)/COPYING $(KDIR)/COPYING.linux
+endef
+
 ### Image scripts ###
 define Build/kernel-img
 	perl $(LINUX_DIR)/scripts/mkknlimg $@ $@.tmp
@@ -21,7 +25,7 @@ endef
 define Build/boot-img
 	rm -f $@.boot
 	mkfs.fat -C $@.boot $(FAT32_BLOCKS)
-	mcopy -i $@.boot $(LINUX_DIR)/COPYING ::COPYING.linux
+	mcopy -i $@.boot $(KDIR)/COPYING.linux ::
 	mcopy -i $@.boot $(KDIR)/bootcode.bin ::
 	mcopy -i $@.boot $(KDIR)/LICENCE.broadcom ::
 	mcopy -i $@.boot $(KDIR)/start.elf ::