This is useful when testing the functionality of the controller from userspace
and there aren't any real SPI slave devices connected to the bus.
Signed-off-by: NMika Westerberg <mika.westerberg@linux.intel.com>
Tested-by: NLu Cao <lucao@marvell.com>
Signed-off-by: NMark Brown <broonie@opensource.wolfsonmicro.com>