alist: Add a function to empty the list

Sometimes it is useful to empty the list without de-allocating any of
the memory used, e.g. when the list will be re-populated immediately
afterwards.

Add a new function for this.

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

include/alist.h

@@ -274,6 +274,13 @@ bool alist_chk_ptr(const struct alist *lst, const void *ptr);
 	     _pos < alist_end(_lst, typeof(*(_pos))); \
 	     _pos++)
 
+/**
+ * alist_empty() - Empty an alist
+ *
+ * This removes all entries from the list, without changing the allocated size
+ */
+void alist_empty(struct alist *lst);
+
 /**
  * alist_init() - Set up a new object list
  *