support Moschip 7840 usb serail driver

Change-Id: I5814cda2750224fb85abac52adc360c84ae8ce3f
Reviewed-on: https://tp-biosrd-v02/gerrit/83196
Reviewed-by: Jamess Huang(黃以民) <Jamess_Huang@asus.com>
Tested-by: Jamess Huang(黃以民) <Jamess_Huang@asus.com>

Author: jamess-huang

arch/arm/configs/miniarm-rk3288_defconfig

@@ -639,6 +639,7 @@ CONFIG_USB_SERIAL_QUALCOMM=y
 CONFIG_USB_SERIAL_SIERRAWIRELESS=y
 CONFIG_USB_SERIAL_OPTION=y
 CONFIG_USB_SERIAL_CH341=y
+CONFIG_USB_SERIAL_MOS7840=y
 CONFIG_USB_GADGET=y
 CONFIG_USB_CONFIGFS=y
 CONFIG_USB_CONFIGFS_ACM=y