HLE: Convert GSP_GPU to ServiceFramework.

The only functional change is the error handling of GSP_GPU::ReadHWRegs function. We previously didn't return error codes (not even for success). The new returns were found by reverse engineering the GSP module.

src/core/hle/service/gsp/gsp.cpp

@@ -0,0 +1,35 @@
+// Copyright 2017 Citra Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#include <vector>
+#include "core/hle/kernel/event.h"
+#include "core/hle/kernel/shared_memory.h"
+#include "core/hle/service/gsp/gsp.h"
+
+namespace Service {
+namespace GSP {
+
+static std::weak_ptr<GSP_GPU> gsp_gpu;
+
+FrameBufferUpdate* GetFrameBufferInfo(u32 thread_id, u32 screen_index) {
+    auto gpu = gsp_gpu.lock();
+    ASSERT(gpu != nullptr);
+    return gpu->GetFrameBufferInfo(thread_id, screen_index);
+}
+
+void SignalInterrupt(InterruptId interrupt_id) {
+    auto gpu = gsp_gpu.lock();
+    ASSERT(gpu != nullptr);
+    return gpu->SignalInterrupt(interrupt_id);
+}
+
+void InstallInterfaces(SM::ServiceManager& service_manager) {
+    auto gpu = std::make_shared<GSP_GPU>();
+    gpu->InstallAsService(service_manager);
+
+    gsp_gpu = gpu;
+}
+
+} // namespace GSP
+} // namespace Service