drm/rockchip: dw_hdmi: add RK3399 HDMI support

RK3399 and RK3288 shared the same HDMI IP controller, only some light
difference with GRF configure.

Signed-off-by: Yakir Yang <ykk@rock-chips.com>
Signed-off-by: Mark Yao <mark.yao@rock-chips.com>
Acked-by: Rob Herring <robh@kernel.org>