LinuxKPI: Add kstrtoll to linux/kstrtox.h

kstrtoll converts a string to a long long.

Sponsored by: Serenity Cyber Security, LLC
MFC after: 1 week
Reviewed by: bz, emaste
Differential Revision: https://reviews.freebsd.org/D45455

(cherry picked from commit d207a2dee332706c352bf35c7e6ecea5240b1ceb)