fix(TL2CHICoupledL2): modify signal io_cpu_halt to io_cpu_wfi (OpenXiangShan#482)

* In top, `io_cpu_halt` is misleading signal, as it may be mistaken for the debug command `halt`.

Author: wissygh

CoupledL2/src/main/scala/coupledL2/tl2chi/TL2CHICoupledL2.scala

@@ -70,7 +70,7 @@ class TL2CHICoupledL2(implicit p: Parameters) extends CoupledL2Base {
 
     val io_chi = IO(new PortIO)
     val io_nodeID = IO(Input(UInt()))
-    val io_cpu_halt = Option.when(cacheParams.enableL2Flush) (IO(Input(Bool())))
+    val io_cpu_wfi = Option.when(cacheParams.enableL2Flush) (IO(Input(Bool())))
 
     // Check port width
     require(io_chi.tx.rsp.getWidth == io_chi.rx.rsp.getWidth);
@@ -265,7 +265,7 @@ class TL2CHICoupledL2(implicit p: Parameters) extends CoupledL2Base {
         linkMonitor.io.nodeID := io_nodeID
         /* exit coherency when: l2 flush of all slices is done and core is in WFI state */
         linkMonitor.io.exitco.foreach { _ :=
-          Cat(slices.zipWithIndex.map { case (s, i) => s.io.l2FlushDone.getOrElse(false.B)}).andR && io_cpu_halt.getOrElse(false.B)
+          Cat(slices.zipWithIndex.map { case (s, i) => s.io.l2FlushDone.getOrElse(false.B)}).andR && io_cpu_wfi.getOrElse(false.B)
         }
 
         /**