arm64: dts: mediatek: asurada: Document GPIO names

Add the gpio-line-names property to gpio-controller in order to
document the usage of GPIOs on the Asurada platform.

Signed-off-by: Nícolas F. R. A. Prado <nfraprado@collabora.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Tested-by: Chen-Yu Tsai <wenst@chromium.org>
Link: https://lore.kernel.org/r/20220629155956.1138955-5-nfraprado@collabora.com


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