bloblist: Add a new function to add or check size

A common check is to see if a blob is present, create it if not and make
sure that the size is large enough. Add a function to handle this.

Signed-off-by: Simon Glass <sjg@chromium.org>

include/bloblist.h

@@ -151,6 +151,19 @@ int bloblist_ensure_size(uint tag, int size, void **blobp);
  */
 void *bloblist_ensure(uint tag, int size);
 
+/**
+ * bloblist_ensure_size_ret() - Find or add a blob
+ *
+ * Find an existing blob, or add a new one if not found
+ *
+ * @tag:	Tag to add (enum bloblist_tag_t)
+ * @sizep:	Size of the blob to create; returns size of actual blob
+ * @blobp:	Returns a pointer to blob on success
+ * @return 0 if OK, -ENOSPC if it is missing and could not be added due to lack
+ *	of space
+ */
+int bloblist_ensure_size_ret(uint tag, int *sizep, void **blobp);
+
 /**
  * bloblist_new() - Create a new, empty bloblist of a given size
  *