drm: Don't call drm_dev_set_unique from platform drivers

Since

commit e112e593
Author: Nicolas Iooss <nicolas.iooss_linux@m4x.org>
Date:   Fri Dec 11 11:20:28 2015 +0100

    drm: use dev_name as default unique name in drm_dev_alloc()

we're using a reasonable default which should work for everyone. Only
mtk, rcar-du and sun4i are affected, and as kms-only drivers without
any rendering support no one should ever care about the unique name

v2: Rebase on top of mediatek.

Cc: Philipp Zabel <p.zabel@pengutronix.de>
Cc: Maxime Ripard <maxime.ripard@free-electrons.com>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Emil Velikov <emil.l.velikov@gmail.com>
Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Acked-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1466499262-18717-5-git-send-email-daniel.vetter@ffwll.ch