In a multi-device system there is no guarantee that the fd being probed
in intel_get_drm_devid() is the same as was opened earlier. Any cache
may outlive the fd, so is frought with lifetime issues. The primary
reason for caching the devid was to avoid extra ioctls in the
dmesg/strace, but hopefully all users now grab the id in their fixture
and not inside every function.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Katarzyna Dec <katarzyna.dec@intel.com>
Reviewed-by: Katarzyna Dec <katarzyna.dec@intel.com>