dt-bindings: pinctrl: update bindings for MT7986 SoC

Add wifi pins in the description and set 'maxItems' for groups and pins.

Reviewed-by: Sam Shih <sam.shih@mediatek.com>
Signed-off-by: Peter Chiu <chui-hao.chiu@mediatek.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220912092440.21011-1-chui-hao.chiu@mediatek.com


Signed-off-by: Linus Walleij <linus.walleij@linaro.org>