spi: Document Octal mode as valid SPI bus width

SPI core supports Octal SPI controllers which have 8 IO lines.
Therefore document 8 as a valid option for spi-tx{rx}-bus-width
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Link: https://lore.kernel.org/r/20200102102118.23318-1-vigneshr@ti.comSigned-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/spi/spi-controller.yaml

@@ -111,7 +111,7 @@ patternProperties:
       spi-rx-bus-width:
         allOf:
           - $ref: /schemas/types.yaml#/definitions/uint32
-          - enum: [ 1, 2, 4 ]
+          - enum: [ 1, 2, 4, 8 ]
           - default: 1
         description:
           Bus width to the SPI bus used for MISO.
@@ -123,7 +123,7 @@ patternProperties:
       spi-tx-bus-width:
         allOf:
           - $ref: /schemas/types.yaml#/definitions/uint32
-          - enum: [ 1, 2, 4 ]
+          - enum: [ 1, 2, 4, 8 ]
           - default: 1
         description:
           Bus width to the SPI bus used for MOSI.