LIBFDT: use memmove() instead of memcpy()

This is partial patch from the DTC/libfdt
commit  67b6b33b9b413a450a72135b5dc59c0a1e33e647
Author: David Gibson <david@gibson.dropbear.id.au>
Date:   Wed Nov 21 11:56:14 2007 +1100

    The patch also fixes one genuine bug caught by valgrind -
    _packblocks() in fdt_rw.c was using memcpy() where it should have been
    using memmove().

Signed-off-by: Gerald Van Baren <vanbaren@cideas.com>