spi: spi-mem: Add SPI_MEM_NO_DATA to the spi_mem_data_dir enum

When defining spi_mem_op templates we don't necessarily know the size
that will be passed when the template is actually used, and basing the
supports_op() check on op->data.nbytes to know whether there will be
data transferred for a specific operation is this not possible.

Add SPI_MEM_NO_DATA to the spi_mem_data_dir enum so that we can base
our checks on op->data.dir instead of op->data.nbytes.

Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>
Reviewed-by: Miquel Raynal <miquel.raynal@bootlin.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

include/linux/spi/spi-mem.h

@@ -57,10 +57,12 @@
 /**
  * enum spi_mem_data_dir - describes the direction of a SPI memory data
  *			   transfer from the controller perspective
+ * @SPI_MEM_NO_DATA: no data transferred
  * @SPI_MEM_DATA_IN: data coming from the SPI memory
  * @SPI_MEM_DATA_OUT: data sent to the SPI memory
  */
 enum spi_mem_data_dir {
+	SPI_MEM_NO_DATA,
 	SPI_MEM_DATA_IN,
 	SPI_MEM_DATA_OUT,
 };