arm: mvebu: turris_omnia: Define CONFIG_ETHPRIME instead of ethact= ENV

CONFIG_ETHPRIME defines primary ethernet device and env variable $ethact
stores currently active ethernet device.

So there is no point to set ethact= in default environment. Instead set
CONFIG_ETHPRIME properly.

Signed-off-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Marek Behún <marek.behun@nic.cz>
diff --git a/configs/turris_omnia_defconfig b/configs/turris_omnia_defconfig
index f310deb..5591c97 100644
--- a/configs/turris_omnia_defconfig
+++ b/configs/turris_omnia_defconfig
@@ -64,6 +64,8 @@
 # CONFIG_SPL_PARTITION_UUIDS is not set
 CONFIG_ENV_OVERWRITE=y
 CONFIG_SYS_RELOC_GD_ENV_ADDR=y
+CONFIG_USE_ETHPRIME=y
+CONFIG_ETHPRIME="ethernet@34000"
 CONFIG_ARP_TIMEOUT=200
 CONFIG_NET_RETRY_COUNT=50
 CONFIG_SPL_OF_TRANSLATE=y