drm/vc4: add extern C guard for the UAPI header

Cc: Eric Anholt <eric@anholt.net>
Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>

include/uapi/drm/vc4_drm.h

@@ -26,6 +26,10 @@
 
 #include "drm.h"
 
+#if defined(__cplusplus)
+extern "C" {
+#endif
+
 #define DRM_VC4_SUBMIT_CL                         0x00
 #define DRM_VC4_WAIT_SEQNO                        0x01
 #define DRM_VC4_WAIT_BO                           0x02
@@ -276,4 +280,8 @@ struct drm_vc4_get_hang_state {
 	__u32 pad[16];
 };
 
+#if defined(__cplusplus)
+}
+#endif
+
 #endif /* _UAPI_VC4_DRM_H_ */