chore(libSceVdecCore): keep shadPS4's licence header on the files taken from it

Export.cpp and include/Api.hpp follow shadPS4's
src/core/libraries/videodec/vdeccore.cpp and vdeccore.h at 0614ce324b,
so they carry those files' SPDX lines, as the libSceAvPlayer files taken
from shadPS4 do.

core/libs/prx/libSceVdecCore/Export.cpp

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: Copyright 2026 shadPS4 Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
 #include "prx/libSceVdecCore/include/Api.hpp"
 #include "prx/libSceVdecCore/include/Decoder.hpp"
 #include <algorithm>

core/libs/prx/libSceVdecCore/include/Api.hpp

@@ -1,3 +1,6 @@
+// SPDX-FileCopyrightText: Copyright 2026 shadPS4 Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
 #pragma once
 
 #include <cstdint>