mx6ulz_14x14_evk: Disable CONFIG_NET

Currently the following build warning is seen:

===================== WARNING ======================
This board does not use CONFIG_DM_ETH (Driver Model
for Ethernet drivers). Please update the board to use
CONFIG_DM_ETH before the v2020.07 release. Failure to
update by the deadline may result in board removal.
See doc/driver-model/migration.rst for more info.
===================================================

Since the mx6ulz-evk board does not have networking support, explicitly
disable networking to avoid the board removal.

Signed-off-by: Fabio Estevam <festevam@gmail.com>
diff --git a/configs/mx6ulz_14x14_evk_defconfig b/configs/mx6ulz_14x14_evk_defconfig
index b854c36..92d73a8 100644
--- a/configs/mx6ulz_14x14_evk_defconfig
+++ b/configs/mx6ulz_14x14_evk_defconfig
@@ -29,6 +29,7 @@
 CONFIG_ENV_IS_IN_MMC=y
 CONFIG_SYS_RELOC_GD_ENV_ADDR=y
 CONFIG_ENV_VARS_UBOOT_RUNTIME_CONFIG=y
+# CONFIG_NET is not set
 CONFIG_DM_74X164=y
 CONFIG_DM_I2C=y
 CONFIG_DM_MMC=y