drm/rockchip: fix coding style and incorrect description

Align with other drivers, tab + 2 space key for description.
and edp/hdmi/dsi can be used on both rk3288 and rk3399.

Signed-off-by: Sandy Huang <hjc@rock-chips.com>
Reviewed-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://patchwork.freedesktop.org/patch/msgid/1535442295-4007-1-git-send-email-hjc@rock-chips.com