riscv: dts: Sync DT with Linux Kernel

Use same dts to boot U-Boot and RISC-V
Linux Kernel v4.16-rc2 in ax25-ae350 platform.

Signed-off-by: Rick Chen <rick@andestech.com>
Signed-off-by: Rick Chen <rickchen36@gmail.com>
Cc: Greentime Hu <green.hu@gmail.com>