SDLC stands for "software development life cycle" or sometimes "system development life cycle," and it refers to the process that you follow for developing your product. There's no single SDLC process that everyone follows -- you're free to define your own, and to change it as the project (or your organization) grows. The point is to have a defined process, preferably one that's written down, that you follow for the work related to development and maintenance of your project. The alternative is to work by the seat of your pants, making things up as you go along.
So, if you want to use Scrum or some other "agile" methodology in your process, that's perfectly fine. Just write it into your SDLC and you're good to go.