powerpc: enabled building with CONFIG_DM=y

powerpc: enabled building with CONFIG_DM=y

Moving to the driver model requires CONFIG_DM to be enabled. Currently
several boards like kmeter1_defconfig produce a build error when CONFIG_DM
is enabled:

In file included from include/common.h:35,
                 from ./arch/powerpc/include/asm/fsl_lbc.h:10,
                 from include/mpc83xx.h:10,
                 from ./arch/powerpc/include/asm/ppc.h:27,
                 from ./arch/powerpc/include/asm/u-boot.h:18,
                 from include/dm/of.h:10,
                 from include/dm/ofnode.h:12,
                 from include/dm/device.h:13,
                 from include/linux/mtd/mtd.h:26,
                 from drivers/mtd/mtdconcat.c:25:
include/image.h: In function ‘image_check_target_arch’:
include/image.h:846:3: error: #error "please define IH_ARCH_DEFAULT in
                       your arch asm/u-boot.h"
 # error "please define IH_ARCH_DEFAULT in your arch asm/u-boot.h"
   ^~~~~
include/image.h:848:31: error: ‘IH_ARCH_DEFAULT’ undeclared (first use in
                        this function); did you mean ‘IH_ARCH_COUNT’?
  return image_check_arch(hdr, IH_ARCH_DEFAULT);

The error can be avoided by moving the definition of IH_ARCH_DEFAULT before

     #include <asm/ppc.h>

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Prabhakar Kushwaha <prabhakar.kushwaha@nxp.com>