os2: remove dependency to gradd.h from IBM's ddk which is non-free:

Add a minimal my_gradd.h containing structures and constants only used
by SDL_os2vman.c -- based on public knowledge from around the internet
including pages from http://www.osfree.org and http://www.edm2.com .

src/video/os2/SDL_os2vman.c

@@ -20,6 +20,7 @@
 */
 #include "../../SDL_internal.h"
 #include "../SDL_sysvideo.h"
+
 #define INCL_DOSERRORS
 #define INCL_DOSPROCESS
 #define INCL_DOSMODULEMGR
@@ -27,15 +28,11 @@
 #define INCL_GPI
 #define INCL_GPIBITMAPS /* GPI bit map functions */
 #include <os2.h>
-#include <gradd.h>
-#if 0 /* not used */
-#define INCL_GRE_DEVICE
-#define INCL_GRE_DEVMISC
-#include <pmddi.h>
-#endif
 #include "SDL_os2output.h"
 #include "SDL_os2video.h"
 
+#include "my_gradd.h"
+
 typedef struct _VODATA {
   PVOID      pBuffer;
   HRGN       hrgnVisible;