kernel: mindspeed: enable additional USB serial drivers

This enables CONFIG_USB_SERIAL_FTDI_SIO (for USB-USB null modem) and
CONFIG_USB_SERIAL_KEYSPAN (already enabled on MIPS).

Change-Id: Ia7387b208efba673e8d497acf6a5e56eb6fb1a91
diff --git a/arch/arm/configs/gfrg200_defconfig b/arch/arm/configs/gfrg200_defconfig
index ffce0fb..b9b0654 100644
--- a/arch/arm/configs/gfrg200_defconfig
+++ b/arch/arm/configs/gfrg200_defconfig
@@ -265,6 +265,8 @@
 CONFIG_USB_SERIAL=y
 CONFIG_USB_SERIAL_CONSOLE=y
 CONFIG_USB_SERIAL_GENERIC=y
+CONFIG_USB_SERIAL_FTDI_SIO=y
+CONFIG_USB_SERIAL_KEYSPAN=y
 CONFIG_USB_SERIAL_PL2303=y
 CONFIG_RTC_CLASS=y
 # CONFIG_RTC_HCTOSYS is not set