arm64: dts: mediatek: cherry: Document gpios and add default pin config

Add gpio-line-names to document GPIO names and add the default basic
pin configuration to allow lower power operation by setting appropriate
state on the unused pins.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: Nícolas F. R. A. Prado <nfraprado@collabora.com>
Link: https://lore.kernel.org/r/20220704101321.44835-7-angelogioacchino.delregno@collabora.com


Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>