LinuxKPI: add lockdep_map

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

Obtained-from: bz_iwlwifi
Sponsored-by: The FreeBSD Foundation
MFC-after: 2 weeks
Reviewed-by: hselasky, emaste
Differential Revision: https://reviews.freebsd.org/D29398