feat(f4): more free memory on handsets with CCM RAM (#5804)

Alternative Lua memory allocator for radios with CCM RAM - primarily GX12 at present

radio/src/lua/custom_allocator.h

@@ -0,0 +1,28 @@
+/*
+ * Copyright (C) EdgeTX
+ *
+ * Based on code named
+ *   opentx - https://github.com/opentx/opentx
+ *   th9x - http://code.google.com/p/th9x
+ *   er9x - http://code.google.com/p/er9x
+ *   gruvin9x - http://code.google.com/p/gruvin9x
+ *
+ * License GPLv2: http://www.gnu.org/licenses/gpl-2.0.html
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
+#pragma once
+
+#if defined(USE_CUSTOM_ALLOCATOR)
+// wrapper for our custom allocator for Lua
+void *custom_l_alloc(void *ud, void *ptr, size_t osize, size_t nsize);
+int custom_avail();
+#endif