LOS ANGELES — Before his death, fans searching online for Prince were likely to find just a handful of his performance videos and almost none of his recorded music. In the days since he died, YouTube and other uploading sites have been flooded with hundreds of hours of the superstar musician’s songs, concert footage, TV appearances and music videos. It’s a boon for Prince lovers, and a sign that the notoriously tight copyright controls the artist maintained over his material are rapidly loosening.