get icenet and testchipip unit tests working

generators/chipyard/src/main/scala/unittest/TestHarness.scala

@@ -0,0 +1,9 @@
+package chipyard.unittest
+
+import chisel3._
+import freechips.rocketchip.config.Parameters
+
+class TestHarness(implicit val p: Parameters) extends Module {
+  val io = IO(new Bundle { val success = Output(Bool()) })
+  io.success := Module(new UnitTestSuite).io.finished
+}

generators/chipyard/src/main/scala/unittest/UnitTestSuite.scala

@@ -0,0 +1,8 @@
+package chipyard.unittest
+
+import freechips.rocketchip.config.Parameters
+import freechips.rocketchip.util.{ElaborationArtefacts, PlusArgArtefacts}
+
+class UnitTestSuite(implicit p: Parameters) extends freechips.rocketchip.unittest.UnitTestSuite {
+  ElaborationArtefacts.add("plusArgs", PlusArgArtefacts.serialize_cHeader)
+}