[POWERPC] Merge libfdt upstream source

This incorporates a copy of dtc libfdt into the kernel source, in
arch/powerpc/boot/libfdt.  This only imports the upstream sources
verbatim, later patches are needed to actually link it into the kernel
Makefiles.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Paul Mackerras <paulus@samba.org>