spi: cadence-quadspi: Add Xilinx Versal external DMA support

Add support to read the data from the flash using external DMA.
Cadence Octal SPI Flash Controller has optional DMA peripheral interface
to communicate indirect mode of operations with external DMA.
Xilinx Versal OSPI has external DMA enabled, this will automatically
request the external DMA to fetch the data from SRAM. It supports only
reading the data from SRAM (DMA read) and doesn't support writing the
data to SRAM (DMA write).
Xilinx Versal OSPI read the data from the flash device using external DMA
and write the data to the flash device using software triggered
indirect mode.

Signed-off-by: Sai Krishna Potthuri <lakshmi.sai.krishna.potthuri@xilinx.com>
Link: https://lore.kernel.org/r/1632478031-12242-5-git-send-email-lakshmi.sai.krishna.potthuri@xilinx.com


Signed-off-by: Mark Brown <broonie@kernel.org>