drm/nouveau: Support devfreq for Tegra

drm/nouveau: Support devfreq for Tegra

Using pmu counters for usage stats. This enables dynamic frequency
scaling on all of the currently supported Tegra gpus.

The register offsets are valid for gk20a, gm20b, gp10b, and gv11b. If
support is added for ga10b, this will need rearchitected.

Signed-off-by: Aaron Kling <webgeek1234@gmail.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>
[fixed tab alignment in gk20a_devfreq_target()]
Signed-off-by: Lyude Paul <lyude@redhat.com>
Link: https://lore.kernel.org/r/20250906-gk20a-devfreq-v2-1-0217f53ee355@gmail.com