Comment # 95 on bug 110674 from Tom B

So here's something interesting. In 5.0.13 there is no function
vega20_display_config_changed.  This function issues
smu_send_smc_msg_with_param(smu, SMU_MSG_NumOfDisplays, 0);

In fact, in 5.0.13 there is no reference at all to SMU_MSG_NumOfDisplays
anywhere in the amdgpu driver. 

Which means, the way that the number of displays is configured is changed in
5.0.13, or done with a hardcoded value instead of a constant.