Add PSCI implementation of hftest_device driver

The hftest_device driver contains board-specific implementation of basic
functionality like rebooting. Now that this is needed for the RPi4
target, add a default, PSCI-based implementation.

Change-Id: Iaf233adcb4cbb4f88a3e720e4c49a94059f8019d
diff --git a/test/hftest/device_psci.c b/test/hftest/device_psci.c
new file mode 100644
index 0000000..fd9a8c5
--- /dev/null
+++ b/test/hftest/device_psci.c
@@ -0,0 +1,24 @@
+/*
+ * Copyright 2020 The Hafnium Authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "hf/arch/vm/power_mgmt.h"
+
+#include "test/hftest.h"
+
+noreturn void hftest_device_reboot(void)
+{
+	arch_reboot();
+}