Bump __FreeBSD_version to 1400015 for LinuxKPI changes.

Commits 17accc08ae15 and de102f870501 add new files to LinuxKPI
which break drm-kmod. In addition various other additions where
comitted. Bump __FreeBSD_version to 1400015 to be able to detect this.

Sponsored by: The FreeBSD Foundation
MFC after: 2 weeks