It really depends on the amount of load that you put on the tempdb database. Everything which is done within the tempdb database is going to be logged in the transaction log just like any other database so if the tempdb database has a very high IO then it may make sense to put the tempdb log on a separate disk. If however the tempdb database isn’t used very much by your databases then putting the log on the same disk as the tempdb data file should be fine.
If you present multiple disks to the tempdb data files with a subset of the tempdb data files on each disk, then present a separate disk for the tempdb log file just to ensure that the log isn’t causing uneven IO load on the disk. Remember that creating multiple log files won’t do anything for you like it does when you have multiple data files as the log files are filled sequentially not in a round robin where the data files are done via a round robin.