MAKEALL: Fix case substitution for old bash

Bash ver 3.x doesn't support the parameter expansion with case
substitution. Use tr instead.
Signed-off-by: NYork Sun <yorksun@freescale.com>
Acked-by: NAllen Martin <amartin@nvidia.com>

MAKEALL

@@ -664,7 +664,7 @@ build_target() {
 	export BUILD_DIR="${output_dir}"
 
 	target_arch=$(get_target_arch ${target})
-	eval cross_toolchain=\$CROSS_COMPILE_${target_arch^^}
+	eval cross_toolchain=\$CROSS_COMPILE_`echo $target_arch | tr '[:lower:]' '[:upper:]'`
 	if [ "${cross_toolchain}" ] ; then
 	    MAKE="make CROSS_COMPILE=${cross_toolchain}"
 	elif [ "${CROSS_COMPILE}" ] ; then