drm/rockchip: vop: add rk3188 vop definitions

The rk3188 has 2 vops not using iommus which only output directly
to a rgb interface per vop. So all other output modes like hdmi
are provided by external brige chips.

Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Reviewed-by: Sandy Huang <hjc@rock-chips.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20180830110937.1739-1-heiko@sntech.de