MCU specific sleep feature is now defined in MCU specific file.

mcu/chx-mkl27z.c

@@ -0,0 +1,23 @@
+extern int chx_allow_sleep;
+
+void
+chx_sleep_mode (int enable_sleep)
+{
+  (void)enable_sleep;
+}
+
+void __attribute__((naked))
+chx_idle (void)
+{
+  int sleep_enabled;
+
+  for (;;)
+    {
+      asm ("ldr	%0, %1" : "=r" (sleep_enabled): "m" (chx_allow_sleep));
+      if (sleep_enabled)
+	{
+	  asm volatile ("wfi" : : : "memory");
+	  /* NOTE: it never comes here.  Don't add lines after this.  */
+	}
+    }
+}