Fix example FIT image source files

The example FIT image source files do not compile with the latest dtc and
mkimage. The following error message is produced:

DTC: dts->dtb  on file "kernel.its"
Error: kernel.its 7:0 - 1:0 syntax error
FATAL ERROR: Unable to parse input tree
./mkimage: Can't read kernel.itb.tmp: Invalid argument

The FIT image source files are missing the "/dts-v1/;" directive at the
beginning of the file. Add the directive to the examples.

Signed-off-by: Ira W. Snyder <iws@ovro.caltech.edu>

doc/uImage.FIT/kernel.its

 /*
  * Simple U-boot uImage source file containing a single kernel
  */
+
+/dts-v1/;
+
 / {
 	description = "Simple image with single Linux kernel";
 	#address-cells = <1>;

doc/uImage.FIT/kernel_fdt.its

 /*
  * Simple U-boot uImage source file containing a single kernel and FDT blob
  */
+
+/dts-v1/;
+
 / {
 	description = "Simple image with single Linux kernel and FDT blob";
 	#address-cells = <1>;

doc/uImage.FIT/multi.its

 /*
  * U-boot uImage source file with multiple kernels, ramdisks and FDT blobs
  */
+
+/dts-v1/;
+
 / {
 	description = "Various kernels, ramdisks and FDT blobs";
 	#address-cells = <1>;

doc/uImage.FIT/update3.its

 /*
  * Example Automatic software update file.
  */
+
+/dts-v1/;
+
 / {
 	description = "Automatic software updates: kernel, ramdisk, FDT";
 	#address-cells = <1>;

doc/uImage.FIT/update_uboot.its

@@ -2,6 +2,9 @@
  * Automatic software update for U-Boot
  * Make sure the flashing addresses ('load' prop) is correct for your board!
  */
+
+/dts-v1/;
+
 / {
 	description = "Automatic U-Boot update";
 	#address-cells = <1>;