separate PWM and basic example into separate packages

src/main/scala/pwm/Top.scala

@@ -0,0 +1,17 @@
+package pwm
+
+import chisel3._
+import example._
+import cde.Parameters
+
+class ExampleTopWithPWM(q: Parameters) extends ExampleTop(q)
+    with PeripheryPWM {
+  override lazy val module = Module(
+    new ExampleTopWithPWMModule(p, this, new ExampleTopWithPWMBundle(p)))
+}
+
+class ExampleTopWithPWMBundle(p: Parameters) extends ExampleTopBundle(p)
+  with PeripheryPWMBundle
+
+class ExampleTopWithPWMModule(p: Parameters, l: ExampleTopWithPWM, b: => ExampleTopWithPWMBundle)
+  extends ExampleTopModule(p, l, b) with PeripheryPWMModule