image: Add a function to modify category information

Add a generic function which can check whether a category has an
entry ID.

Signed-off-by: Naoki Hayama <naoki.hayama@lineo.co.jp>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/include/image.h b/include/image.h
index 10995b8..00f774f 100644
--- a/include/image.h
+++ b/include/image.h
@@ -568,6 +568,15 @@
  */
 const char *genimg_get_cat_desc(enum ih_category category);
 
+/**
+ * genimg_cat_has_id() - Check whether a category has an item
+ *
+ * @category:	Category to check
+ * @id:		Item ID
+ * @return true or false as to whether a category has an item
+ */
+bool genimg_cat_has_id(enum ih_category category, uint id);
+
 int genimg_get_os_id(const char *name);
 int genimg_get_arch_id(const char *name);
 int genimg_get_type_id(const char *name);