LinuxKPI: add HWEIGHT32()

Add HWEIGHT32() macro needed by iwlwifi and while here add the 8/16/64
variants likewise.

Sponsored by: The FreeBSD Foundation
Reviewed by: hselasky
Differential Revision: https://reviews.freebsd.org/D30501

(cherry picked from commit 4cc8a9da491d10f1b4bad6a50730b67dd5e899c7)