drm/i915: Do not try to enable PSR when Panel doesn't suport it.

Also do not cache aux info. That info could be related to another panel.

Reviewed-by: Vijay Purushothaman <vijay.a.purushothaman@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>