The drm-kmod drivers use linuxkpi and end up with /dev/drm being the
canonical path for the devices, but the drm-subtree drivers use drmkpi
which has them appear under /dev/dri like Linux. Thus, adapt path_is_drm
to recognise both on FreeBSD.
This function is only used for logind, which is Linux-specific, but the
presence in common/drm.c suggested that it had to be portable.
Move it to the logind backend for now.
Path check was done on /dev/dri/card and /dev/dri/renderD. However,
/dev/dri/by-path is a thing, and on FreeBSD, /dev/dri/ symlinks to
/dev/drm/.
Relax Linux check to /dev/dri/, and add FreeBSD check for /dev/drm/.
FreeBSD device numbers cannot be used to check the type of a device, as
they are merely unique filesystem IDs.
As the paths we use have been sanitized with realpath, we can simply use
the path to check if a requested file is an evdev or drm device. This
also allows us to make the check before the file is opened.
