spi: dw: Remove Intel Thunder Bay SOC support

Remove Intel Thunder Bay specific code as the product got cancelled and
there are no end customers or users.

Signed-off-by: Nandhini Srikandan <[e-mail]>
Acked-by: Krzysztof Kozlowski <[e-mail]>
Link: https://msgid.link/r/[e-mail]
Signed-off-by: Mark Brown <[e-mail]>

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

···
           - 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: Intel Mount Evans Integrated Management Complex SPI Controller
         const: intel,mountevans-imc-ssi
       - description: AMD Pensando Elba SoC SPI Controller