spi: dw: allow providing own set_cs callback

Allow platform specific drivers to provide their own set_cs callback when
the IP integration requires it.

Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
diff --git a/drivers/spi/spi-dw.h b/drivers/spi/spi-dw.h
index 2cde247..4460130 100644
--- a/drivers/spi/spi-dw.h
+++ b/drivers/spi/spi-dw.h
@@ -112,6 +112,7 @@ struct dw_spi {
 	u32			reg_io_width;	/* DR I/O width in bytes */
 	u16			bus_num;
 	u16			num_cs;		/* supported slave numbers */
+	void (*set_cs)(struct spi_device *spi, bool enable);
 
 	/* Current message transfer state info */
 	size_t			len;