hw/dma: Implement a Xilinx CSU DMA model

hw/dma: Implement a Xilinx CSU DMA model

ZynqMP QSPI supports SPI transfer using DMA mode, but currently this
is unimplemented. When QSPI is programmed to use DMA mode, QEMU will
crash. This is observed when testing VxWorks 7.

This adds a Xilinx CSU DMA model and the implementation is based on
https://github.com/Xilinx/qemu/blob/master/hw/dma/csu_stream_dma.c.
The DST part of the model is verified along with ZynqMP GQSPI model.

Signed-off-by: Xuzhou Cheng <xuzhou.cheng@windriver.com>
Signed-off-by: Bin Meng <bin.meng@windriver.com>
Tested-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
Reviewed-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
Message-id: 20210303135254.3970-2-bmeng.cn@gmail.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>