drm/i915/selftests: Use all physical engines for i915_active

i915_active must track over any engine, so expand the selftest to
iterate over all uabi engines.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191021162146.1686-1-chris@chris-wilson.co.uk