video: rockchip: rk_vop: add rk3288-dp compare string

video: rockchip: rk_vop: add rk3288-dp compare string

In the current rk3288.dtsi file the compatible string for
the DisplayPort(DP) node ends with "edp". The string in the
binding ends with "dp" which conflicts with "cdn-dp" as a
search term. Add "rk3288-dp" as compare string to select
vop_id.

Signed-off-by: Johan Jonker <jbx6244@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Tested-by: Simon Glass <sjg@chromium.org>  # chromebook-jerry
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>