spi: spi-zynqmp-gqspi: transmit dummy circles by using the controller's internal functionality

There is a data corruption issue that occurs in the reading operation
(cmd:0x6c) when transmitting common data as dummy circles.

The gqspi controller has the functionality to send dummy clock circles.
When writing data with the fields [receive, transmit, data_xfer] = [0,0,1]
to the Generic FIFO, and configuring the correct SPI mode, the controller
will transmit dummy circles.

So let's switch to hardware dummy cycles transfer to fix this issue.

Fixes: 1c26372e ("spi: spi-zynqmp-gqspi: Update driver to use spi-mem framework")
Signed-off-by: Quanyang Wang <quanyang.wang@windriver.com>
Reviewed-by: Amit Kumar Mahapatra <amit.kumar-mahapatra@xilinx.com>
Link: https://lore.kernel.org/r/20210408040223.23134-4-quanyang.wang@windriver.com


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