ARM: mediatek: dts: Add UART dts for MT8127 and MT8135 boards

This patch enable UART for MT8127 moose board and MT8135 evalution board.
Adding the dts, these two boards can show log and shell prompts.

Signed-off-by: Eddie Huang <eddie.huang@mediatek.com>
Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>