MAINTAINERS: Add Lukas Wunner as reviewer for vga_switcheroo

I've been contributing to vga_switcheroo for the past two years and by
now am fairly familiar with it, so danvet suggested that I add myself
as reviewer.

While at it, add missing file pattern for vga_switcheroo.h + vgaarb.h
to the DRM and DRM-MISC sections such that get_maintainer.pl returns
dri-devel@ and the drm-misc maintainers.

Suggested-and-acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Link: http://patchwork.freedesktop.org/patch/msgid/ff2320a0790d039e714cf352cf32ec16fa370627.1490623913.git.lukas@wunner.de