spi: Add bindings for Intel Thunder Bay SOC

Add documentation for SPI controller in Intel Thunder Bay SoC.
Signed-off-by: Nandhini Srikandan <nandhini.srikandan@intel.com>
Acked-by: Rob Herring <robh@kernel.org>
Reviewed-by: Serge Semin <fancer.lancer@gmail.com>
Link: https://lore.kernel.org/r/20220713042223.1458-3-nandhini.srikandan@intel.comSigned-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/spi/snps,dw-apb-ssi.yaml

@@ -61,6 +61,8 @@ properties:
           - const: snps,dw-apb-ssi
       - description: Intel Keem Bay SPI Controller
         const: intel,keembay-ssi
+      - description: Intel Thunder Bay SPI Controller
+        const: intel,thunderbay-ssi
       - description: Baikal-T1 SPI Controller
         const: baikal,bt1-ssi
       - description: Baikal-T1 System Boot SPI Controller