Add some native xex2 structs and handling functions

src/xenia/kernel/util/xex2.h

@@ -13,6 +13,15 @@
 #include "xenia/kernel/util/xex2_info.h"
 #include "xenia/memory.h"
 
+namespace xe {
+namespace kernel {
+template<typename T>
+T* xex2_get_opt_header(const xex2_header* header, uint32_t key);
+
+uint32_t xex2_get_header_size(const xex2_header* header);
+} // namespace kernel
+} // namespace xe
+
 typedef struct { int reserved; } xe_xex2_options_t;
 
 struct xe_xex2;