dt-bindings: spi: spi-mt65xx: add support for MT8516

Add binding documentation of spi-mt65xx for MT8516 SOC.
Signed-off-by: Leilk Liu <leilk.liu@mediatek.com>
Reviewed-by: Matthias Brugger <matthias.bgg@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/spi/spi-mt65xx.txt

@@ -10,6 +10,7 @@ Required properties:
     - mediatek,mt8135-spi: for mt8135 platforms
     - mediatek,mt8173-spi: for mt8173 platforms
     - mediatek,mt8183-spi: for mt8183 platforms
+    - "mediatek,mt8516-spi", "mediatek,mt2712-spi": for mt8516 platforms
 
 - #address-cells: should be 1.