Add initial ML507Shell stub based on VC707Shell

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

@@ -94,6 +94,14 @@ object PowerOnResetFPGAOnly {
   }
 }
 
+// ML507 clock generation
+class ml507_sys_clock extends BlackBox {
+  val io = new Bundle {
+    val CLKIN_IN  = Bool(INPUT)
+    val CLKFX_OUT = Clock(OUTPUT)
+  }
+}
+
 //-------------------------------------------------------------------------
 // vc707_sys_clock_mmcm
 //-------------------------------------------------------------------------