drm/i915: Fix the state checker for ICL Y planes

drm/i915: Fix the state checker for ICL Y planes

The plane used to scan out NV12 luma on ICL is logically
off but actually on. Fix the state checker to account for this.

Cc: Imre Deak <imre.deak@intel.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=109457
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190304131217.4338-1-ville.syrjala@linux.intel.com
Reviewed-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>