MAINTAINERS: Shovel drivers/gpu/vga/* to Dave

DRM is pretty much the main user of this stuff (if we ignore the sysfs
interface used by X, i.e. by the same gang of people writing the drm
drivers). So shovel it into Dave's responsibility to avoid patches
getting lost on lkml.

With this get_maintainers will rout vgaarb and switcheroo patches
correctly.

Cc: Alex Williamson <alex.williamson@redhat.com>
Cc: Dave Airlie <airlied@redhat.com>
Cc: linux-kernel@vger.kernel.org
References: https://lkml.org/lkml/2014/5/25/94


Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Dave Airlie <airlied@redhat.com>