drm/i915: Include G4X/VLV/CHV in self refresh status

Add all missing platforms handled by intel_set_memory_cxsr() to the
i915_sr_status debugfs entry.

v2: Add G4X too. (Ville)
    Clarify the change also affects CHV. (Ander)

References: https://bugs.freedesktop.org/show_bug.cgi?id=89792


Signed-off-by: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>