drm/i915: Ignore skl+ for debugfs/i915_sr_status

drm/i915: Ignore skl+ for debugfs/i915_sr_status

There is no easily digestible single self-refresh status bit, so don't
report one for debugfs/i915_sr_status on gen9+. For the moment this
avoids a read of the non-existent WM1_LP_ILK register.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170309142049.16033-1-chris@chris-wilson.co.uk
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>