drm/rockchip: cdn-dp: Convert to drm bridge

Convert it to drm bridge driver, it will be convenient for us to
migrate the connector part to the display driver later.
Considering that some code depend on the connector, the following
changes have been made:
- Only process edid in &drm_bridge_funcs.edid_read(), so no need to
store additional edid info.
- Now cdn_dp_get_sink_capability() only focused on reading DPCD_REV.
- Update bpc info in cdn_dp_bridge_atomic_enable() instead of
cdn_dp_encoder_mode_set(). Actually, the bpc data will be used in
cdn_dp_bridge_atomic_enable().
- Switch to use DRM_BRIDGE_OP_DP_AUDIO helpers.

This patch also convert to use devm_drm_bridge_alloc() API.

Tested with RK3399 EVB IND board.

Signed-off-by: Chaoyi Chen <chaoyi.chen@rock-chips.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://lore.kernel.org/r/20250529071334.441-1-kernel@airkyi.com