[WIP]IFU: build a simple framework

src/main/scala/xiangshan/decoupled-frontend/IFU.scala

+package xiangshan.frontend
+
+import chipsalliance.rocketchip.config.Parameters
+import chisel3._
+import chisel3.util._
+import xiangshan._
+import utils._
+
+class FtqInterface(implicit p: Parameters) extends XSBundle {
+  val startAddr = UInt(64.W)  
+  val target = UInt(64.W)
+  val hit = Bool()
+}
+
+class ICacheMeta
+
+class IFUIO(implicit p: Parameters) extends XSBundle {
+  val FtqInterface 
+  val ICacheInterface
+  val toIbuffer
+  
+}
+
+@chiselName
+class IFU(implicit p: Parameters) extends XSModule
+{
+  val io = IO(new IFUIO)
+  val toFtq    = io.FtqInterface.toFtq
+  val fromtFtq = io.FtqInterface.fromFtq
+
+}