drm/i915: Agnostic INTEL_INFO

Adapt the macro so that we can pass either the struct drm_device or the
struct drm_i915_private pointers and get the answer we want. Over time,
my plan is to convert all users over to using drm_i915_private and so
trimming down the pointer dance. Having spent a few hours chasing that
goal and achieved over 8k of object code saving, it appears to be a
worthwhile target. This interim macro allows us to slowly convert over.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
[danvet: Drop the (struct drm_device *) cast per the m-l discussion.
Also explain the seemingly unecessary first cast.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>