drm/i915/gen9: unconditionally apply the memory bandwidth WA

drm/i915/gen9: unconditionally apply the memory bandwidth WA

Mahesh Kumar is already working on a proper implementation for the
workaround, but while we still don't have it, let's just
unconditionally apply the workaround for everybody and we hope we can
close all those numerous bugzilla tickets. Also, I'm not sure how easy
it will be to backport the final implementation to the stable Kernels,
and this patch here is probably easier to backport.

At the present moment I still don't have confirmation that this patch
fixes any of the bugs listed below, but we should definitely try
testing all of them again.

v2: s/intel_needs_memory_bw_wa/skl_needs_memory_bw_wa/ (Lyude).
v3: Rebase (dev -> dev_priv change on ilk_wm_max_level).

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=94337
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=94605
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=94884
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=95010
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=96226
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=96828
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=97450
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=97830
Cc: stable@vger.kernel.org
Cc: Mahesh Kumar <mahesh1.kumar@intel.com>
Cc: Lyude <cpaul@redhat.com>
Cc: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: Lyude <cpaul@redhat.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1476210338-9797-1-git-send-email-paulo.r.zanoni@intel.com