You don't need to know any coding at all. That being said, the more you know, the more of a leg up you'll have.
I have seen people come in to computer courses in college with no prior knowledge, and still graduate successfully. That being said, they have to work hard, since it means learning an entirely new skill.
Any programming you do learn while still in high school will lead to various advantages. You might be in the position to help teach other students, which is often a really good way to learn more (because when they ask a question you realize you don't know the answer to, you probably will be able to find the answer, and then you both learn). Learning ahead of time also means that if any concepts aren't well-taught in your college, you will both have a chance of already having learned it yourself, and you will probably have the background you need to come to understand it.
If you're looking to get started, and your high school doesn't offer any programming classes (or if it does but you can't take them at the moment), then I recommend codeacademy.com, a free Web site that teaches basic programming. Beyond that, writing programs on your own time, whatever interests you, can get you a long way. I loved writing computer games in high school, and doing so meant that I had already encountered almost all of the hard ideas being taught in my college courses.
So, again, you don't need to know any, but I still recommend learning whatever you can.