RISC-V: Add Jim Wilson as a maintainer

RISC-V: Add Jim Wilson as a maintainer

Jim has recently started working at SiFive, where he'll be contributing
to our GCC port.  Andrew, Kito and I would like him to be a mainatiner.
My understand is that this is the right place to ask.

I've also changed my address to my SiFive one, where I also work -- it
seems cleaner to have everyone use our proper email address.

ChangeLog

2017-11-15  Palmer Dabbelt  <palmer@sifive.com>

        * MAINTAINERS (RISC-V): Add Jim Wilson as a maintainer.
        Use my SiFive email address.

From-SVN: r254774