Update documentation for flat device tree format v17

[Jon Loeliger]

So, like, the other day David Gibson mumbled:
> This patch updates booting-without-of.txt to describe version 17 of
> the flattened device tree format.  Version 17 is a small, backwards
> compatible change from version 16, adding an extra field giving the
> size of the device tree's structure block.  At this time, the kernel
> has no use for the extra information, however its presence can make
> life easier for bootloaders or other software manipulating the tree.
> 
> In addition this patch adds information on the size_dt_strings field
> of the device tree header, present since version 3 of the flattened
> tree format, but omitted from the documentation.  It also makes
> changes to consistently refer to versions 16 and 17 as versions 16 and
> 17 in decimal, rather than version 0x10 which was occasionally used
> for version 16 previously.
> 
> Finally, we also add the new field to the definition of the device
> tree header structure in prom.h
> 
> Signed-off-by: David Gibson <david at gibson.dropbear.id.au>
> ---
> 
> Paulus, please apply.

Paul,

I have applied the Version 17 Updates patch to my DTC tree.

Acked-by: Jon Loeliger <jdl at freescale.com>

Thanks,
jdl