MIPS: Update email address for Marcin Nowakowski

MIPS is no longer part of Imagination Technologies and my @imgtec.com
address will soon stop working. Update any files containing my address
as well as the .mailmap to point to my new @mips.com address.

Signed-off-by: Marcin Nowakowski <marcin.nowakowski@mips.com>
Patchwork: https://patchwork.linux-mips.org/patch/17579/
Signed-off-by: James Hogan <jhogan@kernel.org>