arm64: dts: Add spi bus dts

This patch adds MT8173 spi bus controllers into device tree.

Signed-off-by: Leilk Liu <leilk.liu@mediatek.com>
Reviewed-and-Tested-by: Nicolas Boichat <drinkcat@chromium.org>
Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>