drm/i915/skl: Fix spurious gpu hang with gt3/gt4 revs

Experiments with heaven 4.0 benchmark and skylake gt3e (rev 0xa)
suggest that WaForceContextSaveRestoreNonCoherent is needed for all
revs. Extending this to all revs cures a gpu hang with rev 0xa when
running heaven4.0 gpu benchmark.

We have been here before, with problems enabling gt4e and extending
up to revision F0 instead of false claims of bspec of E0 only. See
commit <e238659ddd88> ("drm/i915/skl: Default to noncoherent access
up to F0"). In retrospect we should have covered this with this big
blanket back then already, as E0 vs F0 discrepancy was suspicious
enough.

Previously the WaForceEnableNonCoherent has been tied to
context non-coherence, atleast in relevant hsds. So keep this tie
and extended this alongside.

Cc: Abdiel Janulgue <abdiel.janulgue@linux.intel.com>
Cc: Ben Widawsky <benjamin.widawsky@intel.com>
Cc: Timo Aaltonen <tjaalton@ubuntu.com>
Cc: stable@vger.kernel.org
Reported-by: Mike Lothian <mike@fireburn.co.uk>
References: https://bugs.freedesktop.org/show_bug.cgi?id=93491
Signed-off-by: Mika Kuoppala <mika.kuoppala@intel.com>
Reviewed-by: Ben Widawsky <benjamin.widawsky@intel.com>
Tested-by: Timo Aaltonen <tjaalton@ubuntu.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1459860977-27751-2-git-send-email-mika.kuoppala@intel.com
(cherry picked from commit 97ea6be161c55dec896b65c95157d953c330ae05)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>