service: Add skeleton for psm service

Seems to be the power controller. Listed in switchbrew under the category PTM services.

src/core/hle/service/ptm/psm.h

@@ -0,0 +1,22 @@
+// Copyright 2018 yuzu emulator team
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#pragma once
+#include "core/hle/service/service.h"
+
+namespace Service::SM {
+class ServiceManager;
+}
+
+namespace Service::PSM {
+
+class PSM final : public ServiceFramework<PSM> {
+public:
+    explicit PSM();
+    ~PSM() override;
+};
+
+void InstallInterfaces(SM::ServiceManager& sm);
+
+} // namespace Service::PSM