I think you will want to get Sunfire over Cinderhulk. Pretty much everyone who runs TP/Smite have built in gap closer. Garen has none. That said, challenging smite could be helpful simply to live longer or chilling smite (whatever the current name is) can help you gap close a little. This doesn't fix though if you get caught you have no way to escape. You need the flash/ghost to escape in this instance. The big champions who do this are Shyvanna/Hecarim. This is because they have natural gap closers that can double as escapes as well. Whatever you do, never run TP/Flash.
In conclusion, the main reason you can't run smite on Garen is his lack of gap closer. Even if the scaling health ends up being better late game it still doesn't bring what you get from flash/ghost. Get Sunfire and start off farming chicken camp if you want that level 2. He should be able to solo that relatively easy.
EDIT: You can make it be viable taking the TP/Smite. Essentially you will try to make yourself a strong duelist with challenging smite and attempt to force their team to split up for your team to take objectives. You need to ward really well to avoid being caught since you have no escape. This allows you to still join team fights and put pressure elsewhere. This is probably the best playstyle IF you actually want to run TP/Smite but I recommend against it. Flash+TP > TP+Smite > Smite+Flash.