spl: nand: sunxi: use PIO instead of DMA

spl: nand: sunxi: use PIO instead of DMA

SPL support was first written to support only the earlier generations of
Allwinner SoCs, and was only really enabled on the A13 / GR8. However,
those old SoCs had a DMA engine that has been replaced since the A31 by
another DMA controller that is no longer compatible.

Since the code directly uses that DMA controller, it cannot operate
properly on the later SoCs, while the NAND controller has not changed.

There's two paths forward, the first one would have been to add support
for that DMA controller too, the second to just remove the DMA usage
entirely and rely on PIO.

The later has been chosen because CPU overload at this stage is not an
issue and it makes the driver more generic, and easier to understand.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Acked-by: Boris Brezillon <boris.brezillon@bootlin.com>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>