RFC: switch the remaining architectures to use generic GUP v2

[David Miller]

From: Christoph Hellwig <hch at lst.de>
Date: Sat,  1 Jun 2019 09:49:43 +0200

> below is a series to switch mips, sh and sparc64 to use the generic
> GUP code so that we only have one codebase to touch for further
> improvements to this code.  I don't have hardware for any of these
> architectures, and generally no clue about their page table
> management, so handle with care.
> 
> Changes since v1:
>  - fix various issues found by the build bot
>  - cherry pick and use the untagged_addr helper form Andrey
>  - add various refactoring patches to share more code over architectures
>  - move the powerpc hugepd code to mm/gup.c and sync it with the generic
>    hup semantics

I will today look seriously at the sparc64 stuff wrt. tagged pointers.