remove set_fs for riscv v2

[Christoph Hellwig]

On Tue, Sep 08, 2020 at 09:59:29PM -0700, Palmer Dabbelt wrote:
>>
>> The first four patches are general improvements and enablement for all nommu
>> ports, and might make sense to merge through the above base branch.
>
> Seems like it to me.  These won't work without the SET_FS code so I'm OK if you
> guys want to keep them all together.  Otherwise I think I'd need to wait until
> the SET_FS stuff gets merged before taking any of these, which would be a bit
> of a headache.

now that we've sorted out a remaining issue base.set_fs should not
be rebased any more, so you could pull it into the riscv tree or a topic
branch.

The first four patch should go into base.set_fs, though.  Arnd, can you
re-review the updated patches?