arm64: dts: mediatek: mt8395-nio-12l: add PMIC and GPIO keys support

arm64: dts: mediatek: mt8395-nio-12l: add PMIC and GPIO keys support

Add support for PMIC and GPIO keys on the Radxa NIO 12L board:
Declare a gpio-keys node for the Volume Up button using GPIO106.
Add the corresponding pin configuration in the pinctrl node.
Add a mediatek,mt6359-keys subnode under the PMIC to handle the
power and home buttons exposed by the MT6359.

Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: Julien Massot <julien.massot@collabora.com>
Link: https://lore.kernel.org/r/20250905-radxa-nio-12-l-gpio-v3-2-40f11377fb55@collabora.com
Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>