Convert CONFIG_NETCONSOLE to Kconfig

This converts the following to Kconfig:
   CONFIG_NETCONSOLE

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/nitrogen6s_defconfig b/configs/nitrogen6s_defconfig
index 71dff7a..b28cd64 100644
--- a/configs/nitrogen6s_defconfig
+++ b/configs/nitrogen6s_defconfig
@@ -46,6 +46,7 @@
 CONFIG_ENV_OVERWRITE=y
 CONFIG_ENV_IS_IN_SPI_FLASH=y
 CONFIG_SYS_RELOC_GD_ENV_ADDR=y
+CONFIG_NETCONSOLE=y
 CONFIG_DM=y
 CONFIG_USB_FUNCTION_FASTBOOT=y
 CONFIG_FASTBOOT_BUF_ADDR=0x12000000