nitrogen6x: config: add gpio command

Enable the 'gpio' command to allow reading and toggling of GPIO
pins.

Signed-off-by: Eric Nelson <eric.nelson@boundarydevices.com>
diff --git a/include/configs/nitrogen6x.h b/include/configs/nitrogen6x.h
index 60c942f..21013bc 100644
--- a/include/configs/nitrogen6x.h
+++ b/include/configs/nitrogen6x.h
@@ -32,6 +32,7 @@
 #define CONFIG_BOARD_EARLY_INIT_F
 #define CONFIG_MISC_INIT_R
 #define CONFIG_MXC_GPIO
+#define CONFIG_CMD_GPIO
 #define CONFIG_CI_UDC
 #define CONFIG_USBD_HS
 #define CONFIG_USB_GADGET_DUALSPEED