dtc: Use libfdt/fdt.h instead of flat_dt.h

[Jon Loeliger]

So, like, the other day David Gibson mumbled:
> In the dtc tree, both flat_dt.h and libfdt/fdt.h have structures and
> constants relating to the flattened device tree format derived from
> asm-powerpc/prom.h in the kernel.  The former is used in dtc, the
> latter in libfdt.
> 
> libfdt/fdt.h is the more recent, revised version, so use that
> throughout, removing flat_dt.h.
> 
> Signed-off-by: David Gibson <david at gibson.dropbear.id.au>

Applied.

As instructed, I also ignored this patch:
    dtc: Use a custom name for lexer output

Thanks,
jdl