dt-bindings: pinctrl: update uart/mmc bindings for MT7986 SoC

dt-bindings: pinctrl: update uart/mmc bindings for MT7986 SoC

Fix mmc and uart pins after uart splitting.

Some pinmux pins of the mt7986 pinctrl driver is composed of multiple
pinctrl groups, the original binding only allows one pinctrl group
per dts node, this patch sets "maxItems" for these groups and add new
examples to the binding documentation.

Fixes: 65916a1ca90a ("dt-bindings: pinctrl: update bindings for MT7986 SoC")
Signed-off-by: Sam Shih <sam.shih@mediatek.com>
Signed-off-by: Frank Wunderlich <frank-w@public-files.de>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20221106080114.7426-3-linux@fw-web.de
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>