arm64: defconfig: enable support for serial port connected device

This patch enables these configs:

+CONFIG_SERIAL_DEV_BUS=y
+CONFIG_SERIAL_DEV_CTRL_TTYPORT=y

As example, a bluetooth device connected to UART port can be supported by
this.
Signed-off-by: NGuodong Xu <guodong.xu@linaro.org>
Signed-off-by: NWei Xu <xuwei5@hisilicon.com>

arch/arm64/configs/defconfig

@@ -252,6 +252,8 @@ CONFIG_SERIAL_MSM_CONSOLE=y
 CONFIG_SERIAL_XILINX_PS_UART=y
 CONFIG_SERIAL_XILINX_PS_UART_CONSOLE=y
 CONFIG_SERIAL_MVEBU_UART=y
+CONFIG_SERIAL_DEV_BUS=y
+CONFIG_SERIAL_DEV_CTRL_TTYPORT=y
 CONFIG_VIRTIO_CONSOLE=y
 CONFIG_I2C_CHARDEV=y
 CONFIG_I2C_MUX=y