drm/i915/selftests: Check we can recover a wedged device

After declaring a terminally wedged device, we allow ourselves to
recover on the next GPU reset (manually triggered), or resume. Check
that resetting a wedged device does work.

v2: Add rpm (taken explicitly in the subtest in case we remove the outer
wakeref) and early warning to i915_reset() for missed wakerefs

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181213091522.2926-1-chris@chris-wilson.co.uk