drm/i915: Disable decoupled MMIO

commit 4c4c565 upstream.

The decoupled MMIO feature doesn't work as intended by HW team. Enabling
it with forcewake will only make debugging efforts more difficult, so
let's disable it.

Fixes: 85ee17e ("drm/i915/bxt: Broxton decoupled MMIO")
Cc: Zhe Wang <zhe1.wang@intel.com>
Cc: Praveen Paneri <praveen.paneri@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Daniel Vetter <daniel.vetter@intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: intel-gfx@lists.freedesktop.org
Signed-off-by: Kai Chen <kai.chen@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170523215812.18328-2-kai.chen@intel.com
(cherry picked from commit 0051c10)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/gpu/drm/i915/i915_pci.c

@@ -389,7 +389,6 @@ static const struct intel_device_info intel_skylake_gt3_info = {
 	.has_hw_contexts = 1, \
 	.has_logical_ring_contexts = 1, \
 	.has_guc = 1, \
-	.has_decoupled_mmio = 1, \
 	.has_aliasing_ppgtt = 1, \
 	.has_full_ppgtt = 1, \
 	.has_full_48bit_ppgtt = 1, \