drm/i915: MI_PREDICATE_RESULT_2 is HSW only

drm/i915: MI_PREDICATE_RESULT_2 is HSW only

The MI_PREDICATE_RESULT_2 register exits only on HSW. On other
platforms the same offset is either reserved, or contains some
other register. So write the register only on HSW.

This regression has been introduced in

commit ade1a85a92d5087d66e0c572605f6a8056db19d1
Author: Rodrigo Vivi <rodrigo.vivi@gmail.com>
Date:   Wed Aug 28 16:45:46 2013 -0300

    drm/i915: Report enabled slices on Haswell GT3

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
[danvet: Add regression notice.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>