drm/i915/selftests: recreate WA lists inside the selftest

By using the wa lists inside the live driver structures, we won't
catch issues where those are incorrectly setup or corrupted.
To cover this gap, update the workaround framework to allow saving the
wa lists to independent structures and use them in the selftests.

Suggested-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190110013232.8972-1-daniele.ceraolospurio@intel.com
[tursulin: Fixup checkpatch whitespace complaint in memset.]