Add xlnx_dpdma_read_descriptor() and
xlnx_dpdma_write_descriptor() functions.
xlnx_dpdma_read_descriptor() combines reading a
descriptor from desc_addr by calling dma_memory_read()
and swapping the desc fields from guest memory order
to host memory order. xlnx_dpdma_write_descriptor()
performs similar actions when writing a descriptor.
Found by Linux Verification Center (linuxtesting.org) with SVACE.
Fixes: d3c6369a96 ("introduce xlnx-dpdma")
Signed-off-by: Alexandra Diupina <adiupina@astralinux.ru>
[PMM: tweaked indent, dropped behaviour change for write-failure case]
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
fdf029762f