arm64: defconfig: Enable USB_SERIAL_CP210X

Some hardware platforms required CP20x USB to Serial converter
in order to work onboard functionalities like Bluetooth.

An example of such a platform is from Engicam's PX30 (ARM64).

Mark it as module in defconfig.
Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
Link: https://lore.kernel.org/r/20201109181017.206834-10-jagan@amarulasolutions.comSigned-off-by: Heiko Stuebner <heiko@sntech.de>

arch/arm64/configs/defconfig

@@ -750,6 +750,7 @@ CONFIG_USB_CHIPIDEA_UDC=y
 CONFIG_USB_CHIPIDEA_HOST=y
 CONFIG_USB_ISP1760=y
 CONFIG_USB_SERIAL=m
+CONFIG_USB_SERIAL_CP210X=m
 CONFIG_USB_SERIAL_FTDI_SIO=m
 CONFIG_USB_HSIC_USB3503=y
 CONFIG_NOP_USB_XCEIV=y