Ensure progress for dma_fence_array

[Christian König]

Hi guys,

as pointed out by Chia-I userspace doesn't see any progress when
signaling is not enabled and Boris noted that this is because
dma_fence_array_signaled() never returns true in this case.

Improve this by fixing the dma_fence_array_signaled() implementation to
also return true even if signaling was never explicitely enabled.

We should probably adjust the documentation as well that when the
callback is implemented it should make progess visible even without
enabling signaling.

Please test and review,
Christian.