Allow LogPerfControl to be reused if necessary (OpenXiangShan#261)

Since chipsalliance/chisel#3753, the users
are able to check whether a Data is visible in the current context.
To avoid a large number of duplicated LogPerfControl modules, we
allow it to be reused when some previous instance is still visible
to the current context.

Call `LogPerfControl.reuse(DataMirror.isVisible)` instead of pure
`apply()` to allow the reuse.

However, this is still a temporary workaround. In the future, we
need some clean methods to extract the simulation environment and
access these signals during simulation, possibly via XMR.

src/main/scala/common/LogPerfControl.scala

@@ -25,7 +25,7 @@ class LogPerfControl extends Bundle {
   val dump = Bool()
 }
 
-class LogPerfHelper extends BlackBox with HasBlackBoxInline {
+private class LogPerfHelper extends BlackBox with HasBlackBoxInline {
   val io = IO(Output(new LogPerfControl))
 
   val verilog =
@@ -57,4 +57,9 @@ object LogPerfControl {
   def apply(): LogPerfControl = {
     Module(new LogPerfHelper).io
   }
+
+  private val instances = scala.collection.mutable.ListBuffer.empty[LogPerfControl]
+  def reuse(checker: LogPerfControl => Boolean): LogPerfControl = {
+    instances.find(checker).getOrElse(instances.addOne(apply()).last)
+  }
 }