spi: dt-bindings: Add compatible for MediaTek MT8188

This commit adds dt-binding documentation of spi bus for MediaTek MT8188
SoC platform.
Signed-off-by: Johnson Wang <johnson.wang@mediatek.com>
Link: https://lore.kernel.org/r/20220715120114.4243-1-johnson.wang@mediatek.comSigned-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/spi/mediatek,spi-mt65xx.yaml

@@ -34,6 +34,7 @@ properties:
       - items:
           - enum:
               - mediatek,mt7986-spi-ipm
+              - mediatek,mt8188-spi-ipm
           - const: mediatek,spi-ipm
       - items:
           - enum: