spi: dt-bindings: snps,dw-apb-ssi.yaml: update compatible property

updated compatible property to include "thead,th1520-spi" for the
TH1520 SoC SPI Controller.
Signed-off-by: Kanak Shilledar <kanakshilledar@gmail.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://patch.msgid.link/20240701121355.262259-3-kanakshilledar@gmail.comSigned-off-by: Mark Brown <broonie@kernel.org>

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

@@ -88,6 +88,10 @@ properties:
               - renesas,r9a06g032-spi # RZ/N1D
               - renesas,r9a06g033-spi # RZ/N1S
           - const: renesas,rzn1-spi   # RZ/N1
+      - description: T-HEAD TH1520 SoC SPI Controller
+        items:
+          - const: thead,th1520-spi
+          - const: snps,dw-apb-ssi
 
   reg:
     minItems: 1