MAINTAINERS: Update the files list for the Etnaviv DRM driver

Cc: Lucas Stach <l.stach@pengutronix.de>
Cc: Russell King <linux+etnaviv@arm.linux.org.uk>
Cc: Christian Gmeiner <christian.gmeiner@gmail.com>
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Acked-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1461279842-28695-7-git-send-email-emil.l.velikov@gmail.com