tools: MediaTek: add MTK boot header generation to mkimage

This patch adds support for MTK boot image generation.

Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/common/image.c b/common/image.c
index 1c3a772..0659133 100644
--- a/common/image.c
+++ b/common/image.c
@@ -166,6 +166,7 @@
 	{	IH_TYPE_FIRMWARE_IVT, "firmware_ivt", "Firmware with HABv4 IVT" },
 	{       IH_TYPE_PMMC,        "pmmc",        "TI Power Management Micro-Controller Firmware",},
 	{	IH_TYPE_STM32IMAGE, "stm32image", "STMicroelectronics STM32 Image" },
+	{	IH_TYPE_MTKIMAGE,   "mtk_image",   "MediaTek BootROM loadable Image" },
 	{	-1,		    "",		  "",			},
 };