TODO list
* Use drm helper APIs to read and parse Rx Capabilities.
* Use drm helper APIs to handle the link training.
* Add support for power domain and suspend/resume.
* Add reset functionality.
* Add clock support.
* Add support for audio.
* Add support for MST mode.
* Add support for change color format.
* Add support for eDP.
* Add support for HDCP.
* Compliance test support.
