you dont need to reveal your history, even if you want to study psych. you will not be working with a clinical population for some years to come, so no need to worry about that just yet.

i am not sure how it works where you are, but in australia we ask about all previous degrees, including incomplete attempts (i work in admissions for the medicine faculty at my uni). we have a number of students who are now training to be surgeons who have started degrees but not completed them. usually they say that the degree they started was not the right fit (especially if they came straight out of school and into uni), but sometimes they will give personal reasons e.g., to look after a family member, needing a job to become more financially stable etc.

i wouldn't encourage you to disclose about your depression unless you absolutely 'must' (and i can't see that this situation would arise right now - maybe later on if you start working with a clinical population). unfortunately, there is still a lot of stigma around to do with mental health stuff, and i've (personally) found it to be a lot worse in the psych department than in any of the other departments i've studied or worked in. this could just be my university, though.