Hikey and Dragonboard 410c both use the ADV7533 chip. This chip provides support for CEC and I think this is correctly hooked up to the HDMI connector (I only checked the Hikey schematic). However I don’t think the software for either board provides support for CEC.
Bubblegum-96 takes different approach, with HDMI is implemented using the SoC’s own HDMI peripheral. Again CEC is hooked up in the schematic diagram and I’m afraid I don’t know what software support there is (and I don’t have any HDMI-CEC hardware to test it with).