Revert "drm/i915: Enable RC6 immediately"

This reverts commit b12e0ee2

 ("drm/i915: Enable RC6 immediately"),
as it was never meant to be sent anywhere other than the bug report for
experimentation.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1469132179-4052-1-git-send-email-chris@chris-wilson.co.uk
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>