drm/xe/display: Don't try to use vram if not available

drm/xe/display: Don't try to use vram if not available

Trying to get bo from vram when vram not available will cause
WARN_ON() hence avoid touching vram if not available.

Signed-off-by: Juha-Pekka Heikkila <juhapekka.heikkila@gmail.com>
Reviewed-by: Michael J. Ruhl <michael.j.ruhl@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>