drm/i915: Show waiter's status on engine dump

When showing the list of waiters, include the task's status so that we
can tell if they have been woken up and are waiting for the CPU, or if
they are still waiting to be woken.

v2: task_state_to_char()

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181121151653.24595-1-chris@chris-wilson.co.uk