The Allwinner A31 has a new SPI controller IP compared to the older Allwinner
SoCs.

It supports DMA, but the driver only does PIO for now, and DMA will be
supported eventually.
Signed-off-by: NMaxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: NMark Brown <broonie@linaro.org>