drm: add extern C guard for the UAPI headers

Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
diff --git a/include/uapi/drm/drm_sarea.h b/include/uapi/drm/drm_sarea.h
index 1d1a858..a951ced 100644
--- a/include/uapi/drm/drm_sarea.h
+++ b/include/uapi/drm/drm_sarea.h
@@ -34,6 +34,10 @@
 
 #include "drm.h"
 
+#if defined(__cplusplus)
+extern "C" {
+#endif
+
 /* SAREA area needs to be at least a page */
 #if defined(__alpha__)
 #define SAREA_MAX                       0x2000U
@@ -83,4 +87,8 @@
 typedef struct drm_sarea drm_sarea_t;
 #endif
 
+#if defined(__cplusplus)
+}
+#endif
+
 #endif				/* _DRM_SAREA_H_ */