Enable DisplayPort CEC-Tunneling-over-AUX HDMI support

configname: CONFIG_DRM_DP_CEC

Linux Kernel Configuration
└─>Device Drivers
└─>Graphics support
└─>Direct Rendering Manager (XFree86 4.1.0 and higher DRI support)
└─>Enable DisplayPort CEC-Tunneling-over-AUX HDMI support
In linux kernel since version 3.10 (release Date: 2013-06-30)  
Choose this option if you want to enable HDMI CEC support for
DisplayPort/USB-C to HDMI adapters.

Note: not all adapters support this feature, and even for those
that do support this they often do not hook up the CEC pin.