dw: spi: add support for Amazon's Alpine spi controller

Add support for a new devicetree compatible string called
'amazon,alpine-apb-ssi', which is necessary for the Amazon Alpine spi
controller. 'amazon,alpine-dw-apb-ssi' is used in the dw spi driver if
specified in the devicetree.  Otherwise, fall back to driver default
behavior, i.e. original dw IP hw driver behavior.

Signed-off-by: Talel Shenhar <talel@amazon.com>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Mark Brown <broonie@kernel.org>
diff --git a/drivers/spi/spi-dw.h b/drivers/spi/spi-dw.h
index 0168b083..c9c1588 100644
--- a/drivers/spi/spi-dw.h
+++ b/drivers/spi/spi-dw.h
@@ -32,6 +32,7 @@
 #define DW_SPI_IDR			0x58
 #define DW_SPI_VERSION			0x5c
 #define DW_SPI_DR			0x60
+#define DW_SPI_CS_OVERRIDE		0xf4
 
 /* Bit fields in CTRLR0 */
 #define SPI_DFS_OFFSET			0
@@ -109,6 +110,7 @@ struct dw_spi {
 	u32			fifo_len;	/* depth of the FIFO buffer */
 	u32			max_freq;	/* max bus freq supported */
 
+	int			cs_override;
 	u32			reg_io_width;	/* DR I/O width in bytes */
 	u16			bus_num;
 	u16			num_cs;		/* supported slave numbers */