LinuxKPI: add linux/pm_qos.h

Add a linux/pm_qos.h with three dummy functions and a struct as needed
by a driver and drm-kmod [1] in main with no intend to support this for
the moment.

Submitted by: wulf (drm-kmod bits) [1]
Sponsored by: The FreeBSD Foundation (drm-kmod requested updates)
Reviewed by: hselasky (earlier version), wulf
Differential Revision: https://reviews.freebsd.org/D34234

(cherry picked from commit fa6d3522b56d482e77740e325b59019e2ffc347e)