si.graphics() tie GPU controller to display (and/or vice versa)

[mboudreau]

Is your feature request related to a problem? Please describe.
We're trying to categorize the GPUs as "primary", "secondary", "tertiary", etc and we can do this somewhat based on the bus name and address, but an even better way would be based on which display is being displayed by which GPU.

Describe the solution you'd like
if the displays could have an ID/index/busId or the whole GPU object within it, that would make it super easy to figure out which ones the primary GPU

Describe alternatives you've considered
Currently, we're basing it off the bus name and bus address, but this isn't always correct.

Additional context
We used to do it based on the index it came through, but that's not always accurate and has the possibility of changing over time. We need a way to figure out which cards are currently active/in use to be able to make an assumption of which ones are primary/secondary.