drm/i915/gt: Check engine-is-awake on reset later

As we drop the engine-pm on retiring, that may happen while there are
still CS events in the buffer. As such we cannot assert the engine is
still active on reset, until we know that the current request is still
in flight.

Closes: https://gitlab.freedesktop.org/drm/intel/issues/1338


Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Andi Shyti <andi.shyti@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200227204727.2009346-1-chris@chris-wilson.co.uk