drm/i915: restore the early forcewake cleanup

Some BIOS just leak the forcewak bits, which we clean up.
Unfortunately this has been broken in

commit 521198a2
Author: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Date:   Fri Aug 23 16:52:30 2013 +0300

    drm/i915: sanitize forcewake registers on reset

To make this work both for resets and for BIOS takeover just add the
forcewake clearing call back to intel_uncore_early_sanitize.

We need to clear the forcewake in early sanitize so that the forcewak
dance in intel_uncore_init (to figure out whether we have mt or legacy
forcewake on ivb) works. That cleanup fits in nicely with the general
topic of early_sanitize to prepare for the very first mmio ops.

Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Reported-by: Jörg Otte <jrg.otte@gmail.com>
Cc: Jörg Otte <jrg.otte@gmail.com>
References: https://lkml.org/lkml/2013/11/16/40


Cc: stable@vger.kernel.org (for 3.12 only)
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>