drm/i915/execlists: Don't apply priority boost for resets

Do not treat reset as a normal preemption event and avoid giving the
guilty request a priority boost for simply being active at the time of
reset.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190507122954.6299-1-chris@chris-wilson.co.uk