ARM: dts: mt8135: enable basic SMP bringup for mt8135

Add arch timer node to enable arch-timer support. MT8135 firmware
doesn't correctly setup arch-timer frequency and CNTVOFF, add
properties to workaround this.

This also set cpu enable-method to enable SMP.

Signed-off-by: Yingjoe Chen <yingjoe.chen@mediatek.com>
Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>