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.com


Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>