drm/rockchip: Use drm_fb_helper_fill_info

drm/rockchip: Use drm_fb_helper_fill_info

This will set an fb name for the first time!

v2: Rebase

Reviewed-by: Noralf Trønnes <noralf@tronnes.org>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Sandy Huang <hjc@rock-chips.com>
Cc: "Heiko Stübner" <heiko@sntech.de>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-rockchip@lists.infradead.org
Link: https://patchwork.freedesktop.org/patch/msgid/20190326132008.11781-17-daniel.vetter@ffwll.ch