nv_services: Correct buffer queue fencing and GPFifo fencing

src/core/hle/service/nvdrv/nvdata.h

@@ -0,0 +1,25 @@
+#pragma once
+
+#include <array>
+#include "common/common_types.h"
+
+namespace Service::Nvidia {
+
+struct Fence {
+    s32 id;
+    u32 value;
+};
+
+static_assert(sizeof(Fence) == 8, "Fence has wrong size");
+
+struct MultiFence {
+    u32 num_fences;
+    std::array<Fence, 4> fences;
+};
+
+enum class NvResult : u32 {
+    Success = 0,
+    TryAgain = 11,
+};
+
+} // namespace Service::Nvidia