spinlock: Add spin_lock_init macro like Linux

Signed-off-by: Xiang Xiao <xiaoxiang@xiaomi.com>

include/nuttx/spinlock.h

@@ -152,6 +152,24 @@ static inline spinlock_t up_testset(FAR volatile spinlock_t *lock)
 }
 #endif
 
+/****************************************************************************
+ * Name: spin_lock_init
+ *
+ * Description:
+ *   Initialize a non-reentrant spinlock object to its initial,
+ *   unlocked state.
+ *
+ * Input Parameters:
+ *   lock  - A reference to the spinlock object to be initialized.
+ *
+ * Returned Value:
+ *   None.
+ *
+ ****************************************************************************/
+
+/* void spin_lock_init(FAR spinlock_t *lock); */
+#define spin_lock_init(l) do { *(l) = SP_UNLOCKED; } while (0)
+
 /****************************************************************************
  * Name: spin_lock
  *