ARM: mediatek: Add earlyprintk support for mt8127 & mt8135

Enable low-level debug for Mediatek mt8127 & mt8135 SoC.

Signed-off-by: Joe.C <yingjoe.chen@mediatek.com>
Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>
ARM: mediatek: Fix description for mediatek SoCs

We support more MediaTek SoCs now, update the description.

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