There are a few options here I think which will depend on your regular routine more than anything.
Firstly the usual way to prevent a bad barking habit, no matter the time of day, is to grit your teeth and ignore it. Eventually he'll realise barking means that you will not come down and he'll stop using it to gain your attention. This means ear plugs, apologies to neighbours and not going down to him to give him his breakfast. This is how I addressed the situation with my own puppy when he barked. This can be eased with a quiet radio as some dogs wake up, dislike the silence and whine or bark. Reinforce this by not going to him if he starts barking on your way to give him breakfast, 10-15 seconds should do.
In addition to this our pup is alarm trained, we turned the volume up on our alarm, so he could hear it. Alarm means we're awake and we're getting up, which means garden, breakfast and fun can happen... It also meant we could push the alarm back at weekends and gained ourselves an extra hour. He'd wait for the alarm before giving a whine (the older he's gotten the less he has barked anyway).
You can, and this is more just to treat the symptoms not the problem itself, think about using a timed feeder. We use these for our pups treat dispersal throughout the day, and we used to use them to feed our cat - most come with an ice pack to keep the food fresher. Obviously this is more for hunger based early rising, as discussed in the comments and won't aid him wanting to go outside.