dmaengine: sun6i: Retrieve channel count/max request from devicetree

dmaengine: sun6i: Retrieve channel count/max request from devicetree

To avoid introduction of a new compatible for each small SoC/DMA controller
variation, move the definition of the channel count to the devicetree.

The number of vchans is no longer explicit, but limited by the highest
port/DMA request number. The result is a slight overallocation for SoCs
with a sparse port mapping.

Signed-off-by: Stefan Brüns <[email protected]>
Acked-by: Maxime Ripard <[email protected]>
Signed-off-by: Vinod Koul <[email protected]>