linuxkpi: pgtable: Add more defines

Needed by drm-kmod

Reviewed by: bz
Obtained from: drm-kmod
Sponsored by: Beckhoff Automation GmbH & Co. KG
Differential Revision: https://reviews.freebsd.org/D36101

(cherry picked from commit fd62b3fa1e82c8de3a1abacd4587fe4142e34d96)