arm64: allwinner: a64: add SPI nodes

The A64 SPI controllers are register compatible to the h3/h5 SPI
controllers.

The A64 has two SPI controllers, each with a single chip select.
The handles for the DMA channels (23/24 for SPI0/SPI1) are omitted,
as the A64 DMA support is currently missing.

Signed-off-by: Stefan Brüns <stefan.bruens@rwth-aachen.de>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>