You could also search the Find a Partner directory. Ways to Search or Filter Company or Products describes the various ways to search. Or you can use the general search bar. Here I did "Cortex-a57 and tool" and then selected "show only content results for Find a Partner at the top". There are more results than shown here.
Alternatively, there is an AArch64 version of the GCC tool chain available from Linaro. There is nothing to stop you building your code with GCC and debugging with DS-5. But as Ronan mentioned, you will need to contact ARM for the ARMv8-A compatible version of DS-5.