include: Add a list empty check function

Implement a list helper function that checks for empty lists.

Reviewed-by: Anup Patel <anup.patel@wdc.com>
Reviewed-by: Xiang W <wxjstz@126.com>
Signed-off-by: Atish Patra <atish.patra@wdc.com>

include/sbi/sbi_list.h

@@ -43,6 +43,17 @@ static inline void __sbi_list_add(struct sbi_dlist *new,
 	next->prev = new;
 }
 
+/**
+ * Checks if the list is empty or not.
+ * @param head List head
+ *
+ * Retruns TRUE if list is empty, FALSE otherwise.
+ */
+static inline bool sbi_list_empty(struct sbi_dlist *head)
+{
+	return head->next == head;
+}
+
 /**
  * Adds the new node after the given head.
  * @param new New node that needs to be added to list.