Fix building with the steamrt/scout SDK

(cherry picked from commit b552f26e6a37dc5a911d1876ce60d8aae3c85e9f)

src/video/kmsdrm/SDL_kmsdrmvideo.h

@@ -33,6 +33,20 @@
 #include <gbm.h>
 #include <EGL/egl.h>
 
+#ifndef DRM_CAP_CURSOR_WIDTH
+#define DRM_CAP_CURSOR_WIDTH    8
+#endif
+#ifndef DRM_CAP_CURSOR_HEIGHT
+#define DRM_CAP_CURSOR_HEIGHT   9
+#endif
+
+#ifndef GBM_FORMAT_ARGB8888
+#define GBM_FORMAT_ARGB8888  ((uint32_t)('A') | ((uint32_t)('R') << 8) | ((uint32_t)('2') << 16) | ((uint32_t)('4') << 24))
+#define GBM_BO_USE_CURSOR   (1 << 1)
+#define GBM_BO_USE_WRITE    (1 << 3)
+#define GBM_BO_USE_LINEAR   (1 << 4)
+#endif
+
 typedef struct SDL_VideoData
 {
     int devindex;     /* device index that was passed on creation */