powerpc: Use scripts/mkuboot.sh instead of 'mkimage'

mkuboot.sh provides a basic wrapper for the 'mkimage' utility. Using
mkuboot.sh provides clearer error reporting and allows a toolchain to
use its own 'mkimage' executable specified by ${CROSS_COMPILE}mkimage.
Additionally, this brings PowerPC in line with other architectures
which already call mkimage via mkuboot.sh.

Signed-off-by: Peter Tyser <[e-mail]>
Signed-off-by: Grant Likely <[e-mail]>

arch/powerpc/boot/wrapper

···
 # cross-compilation prefix
 CROSS=
 
+# mkimage wrapper script
+MKIMAGE=$srctree/scripts/mkuboot.sh
+
 # directory for object and other files used by this script
 object=arch/powerpc/boot
 objbin=$object
···
 case "$platform" in
 uboot)
     rm -f "$ofile"
-    mkimage -A ppc -O linux -T kernel -C gzip -a $membase -e $membase \
+    ${MKIMAGE} -A ppc -O linux -T kernel -C gzip -a $membase -e $membase \
 	$uboot_version -d "$vmz" "$ofile"
     if [ -z "$cacheit" ]; then
 	rm -f "$vmz"
···
     ;;
 cuboot*)
     gzip -f -9 "$ofile"
-    mkimage -A ppc -O linux -T kernel -C gzip -a "$base" -e "$entry" \
+    ${MKIMAGE} -A ppc -O linux -T kernel -C gzip -a "$base" -e "$entry" \
             $uboot_version -d "$ofile".gz "$ofile"
     ;;
 treeboot*)