drm: Reduce verbosity level for drm_core_init() debug message

Currently at the end of drm_core_init() we print

[    0.735185] [drm] Initialized

which does not provide any user information and is only a breadcrumb for
developers, so reduce it from info to debug.
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20161229133729.32673-1-chris@chris-wilson.co.uk

drivers/gpu/drm/drm_drv.c

@@ -924,7 +924,7 @@ static int __init drm_core_init(void)
 	if (ret < 0)
 		goto error;
 
-	DRM_INFO("Initialized\n");
+	DRM_DEBUG("Initialized\n");
 	return 0;
 
 error: