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.h

@@ -0,0 +1,32 @@
+// Copyright 2017 Citra Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#pragma once
+
+#include <cstddef>
+#include <string>
+#include "common/common_types.h"
+#include "core/hle/result.h"
+#include "core/hle/service/gsp/gsp_gpu.h"
+
+namespace Service {
+namespace GSP {
+/**
+ * Retrieves the framebuffer info stored in the GSP shared memory for the
+ * specified screen index and thread id.
+ * @param thread_id GSP thread id of the process that accesses the structure that we are requesting.
+ * @param screen_index Index of the screen we are requesting (Top = 0, Bottom = 1).
+ * @returns FramebufferUpdate Information about the specified framebuffer.
+ */
+FrameBufferUpdate* GetFrameBufferInfo(u32 thread_id, u32 screen_index);
+
+/**
+ * Signals that the specified interrupt type has occurred to userland code
+ * @param interrupt_id ID of interrupt that is being signalled
+ */
+void SignalInterrupt(InterruptId interrupt_id);
+
+void InstallInterfaces(SM::ServiceManager& service_manager);
+} // namespace GSP
+} // namespace Service