[Request] Support for fdinfo metrics on GuC submission platforms

Based on some discussion on MangoHud, a userspace tool for displaying performance metrics, it was recommended to make an Issue here to request support for fdinfo metrics on platforms like DG2.

I guess from https://elixir.bootlin.com/linux/latest/source/drivers/gpu/drm/i915/i915_drm_client.c#L151 this support is not currently implemented, and DG2 uses GuC submission.

This support would really help unify the experience for DG2 (and any future discrete card or future GuC only integrated chip) users as the fdinfo based metrics seems likely to land in MangoHud. And thanks for implementing an unprivileged interface for exposing these metrics in the first place.