dt-bindings: display: rockchip: Fix label name of hdptxphy for RK3588 HDMI TX Controller

The hdptxphy is a combo transmit-PHY for HDMI2.1 TMDS Link, FRL Link, DP
and eDP Link. Therefore, it is better to name it hdptxphy0 other than
hdptxphy_hdmi0, which will be referenced by both hdmi0 and edp0 nodes.

Acked-by: Rob Herring (Arm) <robh@kernel.org>
Signed-off-by: Damon Ding <damon.ding@rock-chips.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20250206030330.680424-2-damon.ding@rock-chips.com