When Mithoon made the song Javeda Zindagi, its music was so good that even though people didn't know what the words Javeda Zindagi meant, or at least what Javeda meant, we just fell for the song. Awesome work by Mithoon for sure.
Anyway, the word Javeda, or Javida, the way they have sung it, actually comes from Arabic word Javid, which means Life. Hence, Javeda/ Javida is living, or eternal.
Since Zindagi is simply 'life', Javeda Zindagi is eternal life, so that the line 'mohabbat to ek javeda zindagi hai' would mean something like 'love is (has) an eternal life', or simply love is eternal, or forever.