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/cmd/spl.c b/cmd/spl.c
index 56051b8..61256f4 100644
--- a/cmd/spl.c
+++ b/cmd/spl.c
@@ -8,6 +8,7 @@
 #include <command.h>
 #include <cmd_spl.h>
 #include <env.h>
+#include <image.h>
 #include <linux/libfdt.h>
 
 DECLARE_GLOBAL_DATA_PTR;