powerpc/85xx: Increase fdt address

Loading the fdt at 0xc00000 fails if the uncompressed kernel image is
greater than 12 MiB, which is quite common with modern kernels and
multiplatform defconfigs.  Move fdtaddr to 0x1e00000 which is just under
the ramdiskaddr on most targets.

Signed-off-by: Scott Wood <oss@buserror.net>
Cc: Peter Tyser <ptyser@xes-inc.com>
Cc: Dirk Eibach <eibach@gdsys.de>
Cc: Andy Fleming <afleming@gmail.com>
Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
Acked-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Reviewed-by: York Sun <york.sun@nxp.com>