dmaengine: sun6i: Add support for Allwinner A23 (sun8i) variant

The A23 SoC has the same dma engine as the A31 (sun6i), with a
reduced amount of endpoints and physical channels. Add the proper
config data and compatible string to support it.

A slight difference in sun8i is an undocumented register needs
to be toggled for dma to function.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>