drm/i915: Use the common register access functions for NOTRACE variants

Detangle the confusion that NOTRACE variants of the register read/write
routines were directly using the raw register access. We need for those
routines to reuse the common code for serializing register access and
ensuring the correct register power states. This is only possible now
that the only routines that required raw access use their own API.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>