dt-bindings: pinctrl: mediatek: mt7622: fix array properties

Some properties (function groups & pins) are meant to be arrays and
should allow multiple entries out of enum sets. Use "items" for those.

Mistake was noticed during validation of in-kernel DTS files.

Fixes: b9ffc18c ("dt-bindings: mediatek: convert pinctrl to yaml")
Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Acked-by: Rob Herring <robh@kernel.org>
Message-ID: <20240423045502.7778-1-zajec5@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>