[RFC] remove arch/sh?

[Christoph Hellwig]

Hi Linus and maintainers,

arch/sh seems pretty much unmaintained these days.  The last time I got
any reply to sh patches from the list maintainers, and the last maintainer
pull request was over a year ago, and even that has been rather sporadic.

In the meantime we've not really seen any updates for new kernel features
and code seems to be bitrotting.