drm/i915/selftests: Fail hangcheck testing if the GPU is wedged

If the GPU is irrecoverably wedged on startup, it means that it failed
on initialisation and we have already tried to reset it but failed. We
can ignore all further testing, as it is already dead. Failing early,
prevents us from slowly failing in our endeavours later and timing out.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180705150214.28316-1-chris@chris-wilson.co.uk