drm/rockchip: Add support for Rockchip Soc LVDS

This adds support for Rockchip soc lvds found on rk3288
Based on the patches from Mark yao and Heiko Stuebner.

Signed-off-by: Mark Yao <mark.yao@rock-chips.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Sandy Huang <hjc@rock-chips.com>
Reviewed-by: Mark Yao <mark.yao@rock-chips.com>
Tested-by: Wadim Egorov <w.egorov@phytec.de>
Link: https://patchwork.freedesktop.org/patch/msgid/1504351737-136042-1-git-send-email-hjc@rock-chips.com
Signed-off-by: Mark Yao <mark.yao@rock-chips.com>