MAINTAINERS: Update git entries for drivers in drm-misc

It's still just an experiment, but one lesson learned from drm-misc is
that not updating MAINTAINERS just leads to confusion. And this is
easy to revert.

Cc: Boris Brezillon <boris.brezillon@free-electrons.com>
Cc: Mark Yao <mark.yao@rock-chips.com>
Cc: Eric Anholt <eric@anholt.net>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: Shawn Guo <shawnguo@kernel.org>
Acked-by: Gerd Hoffmann <kraxel@redhat.com>
Acked-by: Eric Anholt <eric@anholt.net>
Acked-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170228193657.3559-1-daniel.vetter@ffwll.ch