dma: xilinx: Add axidmatest test client code

dma: xilinx: Add axidmatest test client code

The code is used for axidma validation. It is using dma_slave_config
generic API and of_dma framework in dma test client.

Driver is capable to test multiple instances if present
in the hardware design.

Signed-off-by: Kedareswara rao Appana <appanad@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>