drm/i915/selftests: Check recovery from corrupted LRC

Check that we can recover if the LRC is totally corrupted. Based on a
very simple theory that anything that can be adjusted via the context
(i.e. on behalf of the user), should be under the purview of the
per-engine-reset.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200227085723.1961649-13-chris@chris-wilson.co.uk