toradex: common: Use random mac address if toradex config block is missing

Set CONFIG_NET_RANDOM_ETHADDR=y, which sets random eth address in
case there is no toradex config block programmed.
In case of missing toradex config block the generated mac address was
always the same, linked to serial number 0.
Use random generated mac address instead.

Acked-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Tested-by: Marcel Ziswiler <marcel.ziswiler@toradex.com> # Verdin iMX8M Plus
Signed-off-by: Emanuele Ghidoli <emanuele.ghidoli@toradex.com>
Signed-off-by: Francesco Dolcini <francesco.dolcini@toradex.com>
Reviewed-by: Fabio Estevam <festevam@gmail.com>
diff --git a/configs/colibri_imx7_defconfig b/configs/colibri_imx7_defconfig
index d5c8604..58eb431 100644
--- a/configs/colibri_imx7_defconfig
+++ b/configs/colibri_imx7_defconfig
@@ -60,6 +60,7 @@
 CONFIG_ENV_RANGE=0x80000
 CONFIG_SYS_RELOC_GD_ENV_ADDR=y
 CONFIG_ENV_VARS_UBOOT_RUNTIME_CONFIG=y
+CONFIG_NET_RANDOM_ETHADDR=y
 CONFIG_IP_DEFRAG=y
 CONFIG_TFTP_BLOCKSIZE=16352
 CONFIG_USE_IPADDR=y