remove set_fs for riscv

[Christoph Hellwig]

On Fri, Sep 04, 2020 at 08:15:03PM +0200, Arnd Bergmann wrote:
> Is there a bigger plan for the rest? I can probably have a look at the Arm
> OABI code if nobody else working on that yet.

m68knommu seems mostly trivial and not interact much with m68k/mmu,
so that woud be my next target.  All the other seems to share more
code for the mmu and nommu case, so they'd have to be done per arch.

arm would be my first target because it is used widespread, and its
current set_fs implemenetation is very strange.  But given thar you
help maintaining arm SOCs and probably know the arch code much better
than I do I'd be more than happy to leave that to you.