Make linprocfs(5) create /proc/bus/pci/devices/, and linsysfs(5)
create /sys/class/power_supply/. This silences some warnings
from biology/linux-foldingathome.

Reported by: 0mp
MFC after: 2 weeks
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D25557