drm/i915: Resurrect golden context on gen6/7

In

commit 8f0e2b9d
Author: Daniel Vetter <daniel.vetter@ffwll.ch>
Date:   Tue Dec 2 16:19:07 2014 +0100

    drm/i915: Move golden context init into ->init_context

I've shuffled around per-ctx init code a bit for legacy contexts but
accidentally dropped the render state init call on gen6/7. Resurrect
it.

Reported-by: Francisco Jerez <currojerez@riseup.net>
Cc: Francisco Jerez <currojerez@riseup.net>
Cc: Dave Gordon <david.s.gordon@intel.com>
Cc: Thomas Daniel <thomas.daniel@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Reviewed-by: Francisco Jerez <currojerez@riseup.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>