dtc: Correct headers in util.c

[Jon Loeliger]

> Since util.c is used in programs other than full dtc, it shouldn't
> include the full dtc.h, just util.h which has prototypes directly
> relevant to it.  This patch makes the change, and also adds includes
> of the necessary system headers which were previously included
> indirectly by dtc.h.
> 
> Signed-off-by: David Gibson <david at gibson.dropbear.id.au>

Applied.

Thanks,
jdl