mediatek: Use external data in kernel FIT

This is a better approach, that e.g. allows to load much less data
into memory in some situations.

mediatek/image/Makefile

@@ -38,8 +38,8 @@ define Device/Default
   DEVICE_DTS_DIR := $(DTS_DIR)
   DEVICE_DTS_LOADADDR := 0x43f00000
   KERNEL_NAME := Image
-  KERNEL := kernel-bin | lzma | iowrt-kernel-fit lzma
-  KERNEL_INITRAMFS := kernel-bin | lzma | iowrt-kernel-fit lzma
+  KERNEL := kernel-bin | lzma | iowrt-kernel-fit lzma external-static
+  KERNEL_INITRAMFS := kernel-bin | lzma | iowrt-kernel-fit lzma external-static
   KERNEL_LOADADDR = $(loadaddr-y)
   UBINIZE_OPTS := -E 5
   BLOCKSIZE := 128k
@@ -83,7 +83,7 @@ endef
 
 define Device/secure-boot
   SECURE_BOOT := 1
-  KERNEL := kernel-bin | lzma | iopsys-secure-boot | squashfs-encrypt | squashfs-hash | iowrt-kernel-fit lzma
+  KERNEL := kernel-bin | lzma | iopsys-secure-boot | squashfs-encrypt | squashfs-hash | iowrt-kernel-fit lzma external-static
   SECURE_BOOT_ROTPK_KEY_SIZE := 2048
   SECURE_BOOT_ROTPK_KEY_ALG := rsa
   SECURE_BOOT_ROTPK_HASH_ALG := sha256