eDP controller need to declare which vop provide the video source,
and it's defined in GRF registers.

But different chips have different GRF register address, so we need to
create a device data to declare the GRF messages for each chips.
Signed-off-by: Yakir Yang <ykk@rock-chips.com>
Acked-by: Mark Yao <mark.yao@rock-chips.com>
Reviewed-by: Tomasz Figa <tfiga@chromium.org>
Reviewed-by: Sean Paul <seanpaul@chromium.org>