Hold ml507 in reset while clock not locked

src/main/scala/ip/xilinx/Xilinx.scala

@@ -99,6 +99,7 @@ class ml507_sys_clock extends BlackBox {
   val io = new Bundle {
     val CLKIN_IN  = Bool(INPUT)
     val CLKFX_OUT = Clock(OUTPUT)
+    val LOCKED_OUT = Bool(OUTPUT)
   }
 }