Move SPIR-V emission functions to their own header

src/shader_recompiler/backend/bindings.h

@@ -0,0 +1,19 @@
+// Copyright 2021 yuzu Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#pragma once
+
+#include "common/common_types.h"
+
+namespace Shader::Backend {
+
+struct Bindings {
+    u32 unified{};
+    u32 uniform_buffer{};
+    u32 storage_buffer{};
+    u32 texture{};
+    u32 image{};
+};
+
+} // namespace Shader::Backend