drm/i915: Disable waitboosting for mmioflips/semaphores

Since commit a6f766f3 ("drm/i915: Limit ring synchronisation (sw
sempahores) RPS boosts") and commit bcafc4e3 ("drm/i915: Limit mmio
flip RPS boosts") we have limited the waitboosting for semaphores and
flips. Ideally we do not want to boost in either of these instances as no
userspace consumer is waiting upon the results (though a userspace producer
may be stalled trying to submit an execbuf - but in this case the
producer is being throttled due to the engine being saturated with
work). With the introduction of NO_WAITBOOST in the previous patch, we
can finally disable these needless boosts.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1469002875-2335-6-git-send-email-chris@chris-wilson.co.uk