LinuxKPI: add lockdep_map

Add stubs for struct lockdep_map and three accessor functions
used by iwlwifi.

Sponsored by: The FreeBSD Foundation
Reviewed by: hselasky, emaste
Differential Revision: https://reviews.freebsd.org/D29398

(cherry picked from commit f1069375d97384754a9e8ee8bc21a32d3ad10987)