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>
diff --git a/hw/dma/Kconfig b/hw/dma/Kconfig
index 5d6be1a..98fbb1b 100644
--- a/hw/dma/Kconfig
+++ b/hw/dma/Kconfig
@@ -26,3 +26,7 @@
 
 config SIFIVE_PDMA
     bool
+
+config XLNX_CSU_DMA
+    bool
+    select REGISTER