Add nodes uart0 to uart4 and uart6 for hi3660 SoC.
Enable uart3 and uart6, disable uart5, in hikey960 board dts.
On HiKey960:
- UART6 is used as default console, and is wired out through low speed
expansion connector.
- UART3 has RTS/CTS hardware handshake, and is wired out through low
speed expansion connector.
- UART5 is not used in commercial launched boards. So disable it.
- UART4 is connected to Bluetooth, WL1837.