Services: Stubbed APM::OpenSession and the ISession interface.

# Conflicts:
#	src/core/hle/service/am/applet_oe.cpp
#	src/core/hle/service/apm/apm.cpp

src/core/hle/service/apm/apm.h

@@ -9,10 +9,18 @@
 namespace Service {
 namespace APM {
 
+enum class PerformanceMode : u8 {
+    Handheld = 0,
+    Docked = 1,
+};
+
 class APM final : public ServiceFramework<APM> {
 public:
     APM();
     ~APM() = default;
+
+private:
+    void OpenSession(Kernel::HLERequestContext& ctx);
 };
 
 /// Registers all AM services with the specified service manager.