util: add the IdentityModule, useful to dedup wires

src/main/scala/util/IdentityModule.scala

@@ -0,0 +1,24 @@
+// See LICENSE.SiFive for license details.
+
+package freechips.rocketchip.tilelink
+
+import Chisel._
+
+class IdentityModule[T <: Data](gen: T) extends Module
+{
+  val io = new Bundle {
+    val in = gen.cloneType.flip
+    val out = gen.cloneType
+  }
+
+  io.out := io.in
+}
+
+object IdentityModule
+{
+  def apply[T <: Data](x: T): T = {
+    val identity = Module(new IdentityModule(x))
+    identity.io.in := x
+    identity.io.out
+  }
+}