[dtc] Add support for flat device tree format version 17

[Timur Tabi]

David Gibson wrote:
> libfdt defined a new version of the flattened device tree format,
> version 17.  It is backwards compatible with version 16, just adding
> an extra header field giving the size of the blob's structure blob.

Question:

Since the DTB is compatible with V16, then technically U-Boot can work with it.  What 
would happen if U-Boot added some nodes to the DTB, but it didn't update size_dt_struct? 
Would the value of size_dt_struct still be correct?  If not, then does that mean that 
U-Boot should reject V17 DTBs?

-- 
Timur Tabi
Linux Kernel Developer @ Freescale