MAINTAINERS: drm/i915 has a new maintainer team

For a bunch of reasons[1] I've decided to step down as maintainer and
let some other folks enjoy the reputation and hang out in the
spotlight.

Jani is going to stick around with his expertise in kms and having
done the fixes flow for a long time now. Joonas will join and bring in
his knowledge on all things GEM. Rodrigo has been less visible because
he's been doing tons of work taking care of the internal branch, and
it'd be good to have more continuity between these two worlds also on
the maintainer side.

1: They all boil down to: This is going to happen sooner or later
anyway, we have a great team, with the process improvements over the
last few years things work rather well, now is as good as any time to
do this. With that change I'll have more time for other aspects of the
stack development than maintainership.

Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Dave Airlie <airlied@gmail.com>
Acked-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Acked-by: Jani Nikula <jani.nikula@linux.intel.com>
Acked-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20170815160101.1683-1-daniel.vetter@ffwll.ch