MAINTAINERS: 4.12 git pulls by -rc6 or wait

[Dave Airlie]

Just so everyone is aware we are running a hard and fast rule of
everything in linux-next by rc6 this time around, so if your tree is
directly included in linux-next that means everything needs to be in
drm-next by the end of this week.

If your tree is directly included in linux-next I'd still like
everything in that tree by -rc6 even if I haven't gotten a pull
request.

Simply put: pull requests for all driver trees must be in by end of
this week, (I'll probably only get around to pull them all early next
week).

Dave.