drm/exynos: add extern C guard for the UAPI header

Cc: Andrzej Hajda <a.hajda@samsung.com>
Cc: Inki Dae <inki.dae@samsung.com>
Signed-off-by: NEmil Velikov <emil.l.velikov@gmail.com>

include/uapi/drm/exynos_drm.h

@@ -17,6 +17,10 @@
 
 #include "drm.h"
 
+#if defined(__cplusplus)
+extern "C" {
+#endif
+
 /**
  * User-desired buffer creation information structure.
  *
@@ -362,4 +366,8 @@ struct drm_exynos_ipp_event {
 	__u32			buf_id[EXYNOS_DRM_OPS_MAX];
 };
 
+#if defined(__cplusplus)
+}
+#endif
+
 #endif /* _UAPI_EXYNOS_DRM_H_ */