dt-bindings: display: rockchip: dw-hdmi: Add compatible for rk3568 HDMI

Define a new compatible for rk3568 HDMI.
This version of HDMI hardware block needs two new clocks hclk_vio and hclk
to provide phy reference clocks.

Signed-off-by: Benjamin Gaignard <benjamin.gaignard@collabora.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Tested-by: Michael Riesch <michael.riesch@wolfvision.net>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20220422072841.2206452-9-s.hauer@pengutronix.de