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/verdin-imx8mp_defconfig b/configs/verdin-imx8mp_defconfig
index 22b8a33..a95edff 100644
--- a/configs/verdin-imx8mp_defconfig
+++ b/configs/verdin-imx8mp_defconfig
@@ -99,6 +99,7 @@
 CONFIG_USE_ETHPRIME=y
 CONFIG_ETHPRIME="eth0"
 CONFIG_VERSION_VARIABLE=y
+CONFIG_NET_RANDOM_ETHADDR=y
 CONFIG_IP_DEFRAG=y
 CONFIG_TFTP_BLOCKSIZE=4096
 CONFIG_SPL_DM=y