headers: sync drm_sarea.h with airlied/drm-next

Adds the C++ extern guards from
ebbb0e5cfd2ceb1150b1 drm: add extern C guard for the UAPI headers

Generated using `make headers_install` from airlied/drm-next
at commit 2a1720376adda5ecf8e636fbfb05339c7dad1c55

Signed-off-by: Eric Engestrom <eric.engestrom@imgtec.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>

include/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
@@ -81,4 +85,8 @@ typedef struct drm_sarea_drawable drm_sarea_drawable_t;
 typedef struct drm_sarea_frame drm_sarea_frame_t;
 typedef struct drm_sarea drm_sarea_t;
 
+#if defined(__cplusplus)
+}
+#endif
+
 #endif				/* _DRM_SAREA_H_ */