abuf: Provide a way to get the buffer address

In many cases it is useful to get the address of a buffer, e.g. when
booting from it. Add a function to handle this.

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

include/abuf.h

@@ -42,6 +42,14 @@ static inline size_t abuf_size(const struct abuf *abuf)
 	return abuf->size;
 }
 
+/**
+ * abuf_addr() - Get the address of a buffer's data
+ *
+ * @abuf: Buffer to check
+ * Return: address of buffer
+ */
+ulong abuf_addr(const struct abuf *abuf);
+
 /**
  * abuf_set() - set the (unallocated) data in a buffer
  *