LinuxKPI: Automatically enable drm support for devices named "drmn"

This allows replace linux_pci_(un)register_drm_driver calls with driver
renaming to FreeBSD name.

Sponsored by: Serenity CyberSecurity, LLC
MFC after: 1 week
Reviewed by: manu, bz
Differential Revision: https://reviews.freebsd.org/D45906