mkimage: Support automatic creating of a FIT without a .its

At present, when generating a FIT, mkimage requires a .its file containing
the structure of the FIT and referring to the images to be included.

Creating the .its file is a separate step that makes it harder to use FIT.
This is not required for creating legacy images.

Often the FIT is pretty standard, consisting of an OS image, some device
tree files and a single configuration. We can handle this case automatically
and avoid needing a .its file at all.

To start with, support automatically generate the FIT using a new '-f auto'
option. Initially this only supports adding a single image (e.g. a linux
kernel) and a single configuration.

Signed-off-by: Simon Glass <sjg@chromium.org>

doc/mkimage.1

@@ -108,10 +108,15 @@ Provide special options to the device tree compiler that is used to
 create the image.
 
 .TP
-.BI "\-f [" "image tree source file" "]"
+.BI "\-f [" "image tree source file" " | " "auto" "]"
 Image tree source file that describes the structure and contents of the
 FIT image.
 
+This can be automatically generated for some simple cases.
+Use "-f auto" for this. In that case the arguments -d, -A, -O, -T, -C, -a
+and -e are used to specify the image to include in the FIT and its attributes.
+No .its file is required.
+
 .TP
 .BI "\-F"
 Indicates that an existing FIT image should be modified. No dtc
@@ -178,6 +183,15 @@ with unavailable keys are skipped.
 .B -c """Kernel 3.8 image for production devices""" kernel.itb
 .fi
 
+.P
+Create a FIT image containing a kernel, using automatic mode. No .its file
+is required.
+.nf
+.B mkimage -f auto -A arm -O linux -T kernel -C none -a 43e00000 -e 0 \\\\
+.br
+.B -c """Kernel 4.4 image for production devices""" -d vmlinuz kernel.itb
+.fi
+
 .SH HOMEPAGE
 http://www.denx.de/wiki/U-Boot/WebHome
 .PP