drm/i915: Disable decoupled MMIO

drm/i915: Disable decoupled MMIO

commit 4c4c565513cca1c53a12956640b5915727431631 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: 85ee17ebeedd ("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 0051c10acabb631cfd439eae73289e6e4c39b2b7)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>