Transitioning to a new Xtensa port maintainer

[augustine.sterling@gmail.com]

After a long run as the Xtensa port maintainer, it is time for me to move
on.

I nominate Max Filippov [cc'd] as the new maintainer. He has contributed
numerous patches over the years which have required minimal comments from
me.

If there is anything I need to do to facilitate this, let me know. I'm
happy to still review patches when needed.

Thanks,

Sterling Augustine