fdtdec: support pack "kern.dtb" to the end of u-boot.bin

- It provides a way to promise kernel dtb can be loaded successfully
  even when the image is damaged.
- This makes developers easily to add what they what just like a "U-Boot" dtb.
- The kern.dtb file is pack into the end of u-boot.bin while ./dts/kern.dtb
  is exist.

Change-Id: I93a36a9c65ea8719e5610cdcbcc7708e5337c53f
Signed-off-by: Joseph Chen <chenjh@rock-chips.com>

Makefile

@@ -904,13 +904,24 @@ u-boot.bin: u-boot-fit-dtb.bin FORCE
 else ifeq ($(CONFIG_OF_SEPARATE),y)
 ifeq ($(CONFIG_USING_KERNEL_DTB),y)
 u-boot-dtb.bin: u-boot-nodtb.bin dts/dt-spl.dtb FORCE
-else
-u-boot-dtb.bin: u-boot-nodtb.bin dts/dt.dtb FORCE
-endif
 	$(call if_changed,cat)
 
+ifneq ($(wildcard dts/kern.dtb),)
+u-boot-dtb-kern.bin: u-boot-dtb.bin FORCE
+	$(call if_changed,copy)
+u-boot.bin: u-boot-dtb-kern.bin dts/kern.dtb FORCE
+	$(call if_changed,cat)
+else
 u-boot.bin: u-boot-dtb.bin FORCE
 	$(call if_changed,copy)
+endif
+else
+
+u-boot-dtb.bin: u-boot-nodtb.bin dts/dt.dtb FORCE
+	$(call if_changed,cat)
+u-boot.bin: u-boot-dtb.bin FORCE
+	$(call if_changed,copy)
+endif
 else
 u-boot.bin: u-boot-nodtb.bin FORCE
 	$(call if_changed,copy)

include/asm-generic/global_data.h

@@ -83,6 +83,9 @@ typedef struct global_data {
 	struct udevice	*timer;		/* Timer instance for Driver Model */
 #endif
 
+#ifdef CONFIG_USING_KERNEL_DTB
+	const void *fdt_blob_kern;	/* Kernel dtb at the tail of u-boot.bin */
+#endif
 	const void *fdt_blob;		/* Our device tree, NULL if none */
 	void *new_fdt;			/* Relocated FDT */
 	unsigned long fdt_size;		/* Space reserved for relocated FDT */

lib/fdtdec.c

@@ -1284,6 +1284,11 @@ int fdtdec_setup(void)
 #  else
 	/* FDT is at end of image */
 	gd->fdt_blob = (ulong *)&_end;
+
+#    ifdef CONFIG_USING_KERNEL_DTB
+	gd->fdt_blob_kern =
+		(ulong *)((ulong)gd->fdt_blob + fdt_totalsize(gd->fdt_blob));
+#    endif
 #  endif
 # elif defined(CONFIG_OF_BOARD)
 	/* Allow the board to override the fdt address. */