boot/uboot: Add support for dtb.img format

Allow to generate u-boot-dtb.img. This is the same format
as u-boot.img, however, it contains a built-in device-tree.
This file is being loaded by the U-Boot SPL.

Signed-off-by: Jan Viktorin <viktorin@rehivetech.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

boot/uboot/Config.in

@@ -106,6 +106,9 @@ config BR2_TARGET_UBOOT_FORMAT_AIS
 config BR2_TARGET_UBOOT_FORMAT_BIN
 	bool "u-boot.bin"
 
+config BR2_TARGET_UBOOT_FORMAT_DTB_IMG
+	bool "u-boot-dtb.img"
+
 config BR2_TARGET_UBOOT_FORMAT_IMG
 	bool "u-boot.img"
 

boot/uboot/uboot.mk

@@ -45,6 +45,8 @@ else ifeq ($(BR2_TARGET_UBOOT_FORMAT_LDR),y)
 UBOOT_BIN = u-boot.ldr
 else ifeq ($(BR2_TARGET_UBOOT_FORMAT_NAND_BIN),y)
 UBOOT_BIN = u-boot-nand.bin
+else ifeq ($(BR2_TARGET_UBOOT_FORMAT_DTB_IMG),y)
+UBOOT_BIN = u-boot-dtb.img
 else ifeq ($(BR2_TARGET_UBOOT_FORMAT_IMG),y)
 UBOOT_BIN = u-boot.img
 else ifeq ($(BR2_TARGET_UBOOT_FORMAT_IMX),y)