drm/i915: Demote drop_caches_set print

Many tests call this ad naseum now (in an infinite loop, very often).
It clutters the logs. Actually, I'd rather drop it completely...

Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Acked-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_debugfs.c

@@ -2744,7 +2744,7 @@ i915_drop_caches_set(void *data, u64 val)
 	struct i915_vma *vma, *x;
 	int ret;
 
-	DRM_DEBUG_DRIVER("Dropping caches: 0x%08llx\n", val);
+	DRM_DEBUG("Dropping caches: 0x%08llx\n", val);
 
 	/* No need to check and wait for gpu resets, only libdrm auto-restarts
 	 * on ioctls on -EAGAIN. */