[POWERPC] Merge dtc upstream source

This incorporates a copy of dtc into the kernel source, in
arch/powerpc/boot/dtc-src.  This commit only imports the upstream
sources verbatim, a later commit will actually link it into the kernel
Makefiles and use the embedded code during the kernel build.

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