dmaengine: sun6i: support V3s SoC variant

Allwinner V3s has a DMA engine similar to the ones from A31, but with
fewer channels and DRQs.

Add support for it.

Signed-off-by: Icenowy Zheng <icenowy@aosc.xyz>
Acked-by: Chen-Yu Tsai <wens@csie.org>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>