common: Drop image.h from common header

Move this uncommon header out of the common header.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/nios2/lib/bootm.c b/arch/nios2/lib/bootm.c
index e189161..bec18fe 100644
--- a/arch/nios2/lib/bootm.c
+++ b/arch/nios2/lib/bootm.c
@@ -6,6 +6,7 @@
 
 #include <common.h>
 #include <cpu_func.h>
+#include <image.h>
 #include <irq_func.h>
 
 #define NIOS_MAGIC 0x534f494e /* enable command line and initrd passing */