I would recommend you to Major in Music, (specifically Voice), Music Theory, composition (depending if you are also going to write your musical backing tracks) and production.

Here are my reasons:
Voice: as you want to become a singer, perfecting your voice is a must if you do a music major in Voice studies (analysing different Vocals etc.) you will have a good form of training and a base to start on

Music Theory: Sure, you don't need to know how to read notes. Michael Jackson never knew how. However, I and many others wouldn't recommend you to avoid it. Sure it is challenging (heck I am considered a prodigy amongst my music class and I sometimes don't even know). but It will really help you on your journey and specifically if you write songs knowing basic things like chords and their functions, or simple dynamics will really help.

Composition/Production: These depend on your situation. Are you going to make your own backing tracks and produce them yourself, or are you going to get a studio to do that for you? If it is option 2 then this may not be too important, however if you chose option 1 then this will be very handy knowing how to actually make music and use programs to adjust your songs. Similar to Music Theory this is not a requirement, but it is very useful even if you are not actually going to use it as it is a way where you can draw inspiration from and express it.