[new uImage] POWERPC: Split get_fdt() into get and relocate routines

PPC specific FDT blob handling code is divided into two separate routines:

get_fdt()	- find and verify a FDT blob (either raw or image embedded)
fdt_relocate()	- move FDT blob to within BOOTMAP if needed

Signed-off-by: Marian Balakowicz <m8@semihalf.com>
Acked-by: Kumar Gala <galak@kernel.crashing.org>