treewide: include libfdt_env.h before fdt.h

and, if including libfdt.h which includes libfdt_env.h in
the correct order, don't include fdt.h before libfdt.h.

this is needed to get the fdt type definitions set from
the project environment before fdt.h uses them.

Signed-off-by: Kim Phillips <kim.phillips@freescale.com>
Cc: Jerry Van Baren <gvb.uboot@gmail.com>