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 <ptyser@xes-inc.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>

arch/powerpc/boot/wrapper

@@ -43,6 +43,9 @@ gzip=.gz
 # 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
@@ -267,7 +270,7 @@ membase=`${CROSS}objdump -p "$kernel" | grep -m 1 LOAD | awk '{print $7}'`
 case "$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 "$vmz"
@@ -327,7 +330,7 @@ coff)
     ;;
 cuboot*)
     gzip -f -9 "$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*)