meta-facebook: yosemite4: Enable USB serial

Enable USB serial kernel configuration for yosemite4.

Tested:
- check usb-serial devices
root@bmc:~# ls /sys/bus/usb-serial/devices/
ttyUSB0  ttyUSB1  ttyUSB2

Change-Id: Ic92cdd0e2314f40867cb521c2a8d7316b4efb984
Signed-off-by: Delphine CC Chiu <Delphine_CC_Chiu@wiwynn.com>
diff --git a/meta-facebook/meta-yosemite4/recipes-kernel/linux/linux-aspeed/yosemite4.cfg b/meta-facebook/meta-yosemite4/recipes-kernel/linux/linux-aspeed/yosemite4.cfg
index b04b0ff..63bafdd 100644
--- a/meta-facebook/meta-yosemite4/recipes-kernel/linux/linux-aspeed/yosemite4.cfg
+++ b/meta-facebook/meta-yosemite4/recipes-kernel/linux/linux-aspeed/yosemite4.cfg
@@ -46,3 +46,8 @@
 # UART enable threads
 CONFIG_SERIAL_8250_NR_UARTS=9
 CONFIG_SERIAL_8250_RUNTIME_UARTS=9
+# USB SERIAL
+CONFIG_USB_SERIAL=y
+CONFIG_USB_SERIAL_CONSOLE=y
+CONFIG_USB_SERIAL_GENERIC=y
+CONFIG_USB_SERIAL_FTDI_SIO=m