RISC-V: defconfig: Enable CONFIG_SERIAL_8250_DW

Add CONFIG_SERIAL_8250_DW=y, which is a necessary option for
StarFive JH7110 and JH7100 SoCs to boot with serial ports.
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Hal Feng <hal.feng@starfivetech.com>
Acked-by: Palmer Dabbelt <palmer@rivosinc.com>
Link: https://lore.kernel.org/r/20221118011714.70877-9-hal.feng@starfivetech.comSigned-off-by: Palmer Dabbelt <palmer@rivosinc.com>

arch/riscv/configs/defconfig

@@ -123,6 +123,7 @@ CONFIG_MICROSEMI_PHY=y
 CONFIG_INPUT_MOUSEDEV=y
 CONFIG_SERIAL_8250=y
 CONFIG_SERIAL_8250_CONSOLE=y
+CONFIG_SERIAL_8250_DW=y
 CONFIG_SERIAL_OF_PLATFORM=y
 CONFIG_VIRTIO_CONSOLE=y
 CONFIG_HW_RANDOM=y