imx8qxp_mek: Select CONFIG_NET_RANDOM_ETHADDR

Some i.MX8QXP MEK boards do not have MAC address stored
and hang during eth driver probe:

Error: ethernet@5b040000 address not set.

(Board hangs)

To fix this problem select CONFIG_NET_RANDOM_ETHADDR so that
a valid MAC address can be used in such case.

Signed-off-by: Fabio Estevam <festevam@gmail.com>
diff --git a/configs/imx8qxp_mek_defconfig b/configs/imx8qxp_mek_defconfig
index 3569931..e1d87d6 100644
--- a/configs/imx8qxp_mek_defconfig
+++ b/configs/imx8qxp_mek_defconfig
@@ -47,6 +47,7 @@
 CONFIG_DEFAULT_DEVICE_TREE="fsl-imx8qxp-mek"
 CONFIG_ENV_IS_IN_MMC=y
 CONFIG_SYS_RELOC_GD_ENV_ADDR=y
+CONFIG_NET_RANDOM_ETHADDR=y
 CONFIG_SPL_DM=y
 CONFIG_SPL_CLK=y
 CONFIG_CLK_IMX8=y