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/ds109_defconfig b/configs/ds109_defconfig
index e494887..e412e3f 100644
--- a/configs/ds109_defconfig
+++ b/configs/ds109_defconfig
@@ -28,6 +28,7 @@
 CONFIG_USE_ENV_SPI_MAX_HZ=y
 CONFIG_ENV_SPI_MAX_HZ=50000000
 CONFIG_ENV_ADDR=0x3D0000
+CONFIG_NETCONSOLE=y
 CONFIG_DM=y
 CONFIG_MVSATA_IDE=y
 CONFIG_BLK=y