drm/i915/selftests: Ignore self-preemption suppression under gvt

GVT forces single port submission of individual requests. We do not
enjoy the context amalgamation that the test depends upon for setting up
the test (where port 0 has a large number of requests with a priority
change somewhere in the middle). Under single request submission of gvt
it is quite able for the preemption event to occur while another context
is active and so there be a real need to act upon that preemption.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=111108
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Zhenyu Wang <zhenyuw@linux.intel.com>
Acked-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190712082549.25053-1-chris@chris-wilson.co.uk