spi: mediatek: Add bindings for mediatek MT7622 soc platform

This patch adds a DT binding documentation for the MT7622 soc.
Signed-off-by: Leilk Liu <leilk.liu@mediatek.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

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

@@ -4,6 +4,7 @@ Required properties:
 - compatible: should be one of the following.
     - mediatek,mt2701-spi: for mt2701 platforms
     - mediatek,mt6589-spi: for mt6589 platforms
+    - mediatek,mt7622-spi: for mt7622 platforms
     - mediatek,mt8135-spi: for mt8135 platforms
     - mediatek,mt8173-spi: for mt8173 platforms