drm: add DRM_INFO_ONCE() to print a one-time DRM_INFO() message

Just like DRM_INFO(), but only do it once.
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Acked-by: Dave Airlie <airlied@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

include/drm/drmP.h

@@ -199,6 +199,9 @@ int drm_err(const char *func, const char *format, ...);
 #define DRM_INFO(fmt, ...)				\
 	printk(KERN_INFO "[" DRM_NAME "] " fmt, ##__VA_ARGS__)
 
+#define DRM_INFO_ONCE(fmt, ...)				\
+	printk_once(KERN_INFO "[" DRM_NAME "] " fmt, ##__VA_ARGS__)
+
 /**
  * Debug output.
  *