LinuxKPI: Add pci_power querying for drm-kmod

Adds a few struct members and a function to get i915_runtime_pm_status()
to compile in drm-kmod.

Differential Revision: https://reviews.freebsd.org/D36749
Sponsored by: Google, Inc. (GSoC 2022)

(cherry picked from commit 4cb3cb2de2065bccbab65b0139c1be65f1da3fdf)