drm/i915: there's no cxsr on ilk

Already discovered in

commit 5a117db7
Author: Eugeni Dodonov <eugeni.dodonov@intel.com>
Date:   Thu Jan 5 09:34:29 2012 -0200

    drm/i915: there is no pipe CxSR on ironlake

but we've failed to rip out the code from the ironlake specific code.

Reviewed-by: Eugeni Dodonov <eugeni.dodonov@intel.com>
Signed-Off-by: Daniel Vetter <daniel.vetter@ffwll.ch>