drm/i915/selftests: Provide stub reset functions

If a test fails, we quite often mark the device as wedged. Provide the
stub functions so that we can wedge the mock device, and avoid exploding
on test failures.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=109981


Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190319214233.25498-3-chris@chris-wilson.co.uk