drm/i915/selftests: Dump engine state and trace upon hanging after reset

If the engine dies after a reset, and so we fail to submit a request
but need to be interrupted by the CI runner, dump the engine state.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200615165013.22973-2-chris@chris-wilson.co.uk