allwinner: Add h3 spi driver

This driver is compatible with H3/H5/A64.
Test was done on the OrangePi-PC2 board (H5 based), which have a mx25l1606e
spi flash on it, by writing u-boot image, reading it and booting from the spi.
There is still room for improvement especially on reading using the controller
automatic burst which will avoid us to write dummy data to the TX FIFO.
DMA is also not supported as we currently don't support the DMA controller on
those SoCs
Only add a kernel module for it.