dt-bindings: serial: Add compatible for Mediatek MT7986

This commit adds dt-binding documentation of uart for Mediatek MT7986 SoC
Platform.
Signed-off-by: Sam Shih <sam.shih@mediatek.com>
Link: https://lore.kernel.org/r/20210726071439.14248-10-sam.shih@mediatek.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/devicetree/bindings/serial/mtk-uart.txt

@@ -15,6 +15,7 @@ Required properties:
   * "mediatek,mt7622-uart" for MT7622 compatible UARTS
   * "mediatek,mt7623-uart" for MT7623 compatible UARTS
   * "mediatek,mt7629-uart" for MT7629 compatible UARTS
+  * "mediatek,mt7986-uart", "mediatek,mt6577-uart" for MT7986 compatible UARTS
   * "mediatek,mt8127-uart" for MT8127 compatible UARTS
   * "mediatek,mt8135-uart" for MT8135 compatible UARTS
   * "mediatek,mt8173-uart" for MT8173 compatible UARTS