kernel: add _WAIT_Q_INIT()

Dissociate wait queue initialization from doubly-linked lists if the
underlying implementation is to be abstracted.

Change-Id: Id7544c6ac506643437f9c4f0ae97e7eecab8d06d
Signed-off-by: Benjamin Walsh <walsh.benj@gmail.com>
diff --git a/kernel/include/wait_q.h b/kernel/include/wait_q.h
index 0637a96..7a28aed 100644
--- a/kernel/include/wait_q.h
+++ b/kernel/include/wait_q.h
@@ -42,6 +42,8 @@
 #define _get_next_timeout_expiry() (K_FOREVER)
 #endif
 
+#define _WAIT_Q_INIT(wait_q) SYS_DLIST_STATIC_INIT(wait_q)
+
 #ifdef __cplusplus
 }
 #endif