SPL: common/Makefile: Add image.c to SPL build

This is needed for the SPEAr SPL support, as SPEAr uses the mkimage
header to wrap and validate the images (SPL & U-Boot).

Signed-off-by: Stefan Roese <sr@denx.de>
diff --git a/common/Makefile b/common/Makefile
index 31175e3..483eb4d 100644
--- a/common/Makefile
+++ b/common/Makefile
@@ -31,7 +31,6 @@
 COBJS-y += command.o
 COBJS-y += exports.o
 COBJS-$(CONFIG_SYS_HUSH_PARSER) += hush.o
-COBJS-y += image.o
 COBJS-y += s_record.o
 COBJS-$(CONFIG_SERIAL_MULTI) += serial.o
 COBJS-y += xyzModem.o
@@ -191,6 +190,7 @@
 endif
 COBJS-y += console.o
 COBJS-y += dlmalloc.o
+COBJS-y += image.o
 COBJS-y += memsize.o
 COBJS-y += stdio.o