arm64: dts: mediatek: mt7986a-bpi-r3: Set interrupt-parent to mdio switch

arm64: dts: mediatek: mt7986a-bpi-r3: Set interrupt-parent to mdio switch

Being this an interrupt controller, the binding forbids to use
interrupts-extended and wants an `interrupts` property instead.

Since this interrupt controller's parent is on the GPIO controller
set it as interrupt-parent and change interrupts-extended to just
interrupts to silence a dtbs_check warning.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20250724083914.61351-26-angelogioacchino.delregno@collabora.com
Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>