Kconfig: Move CONFIG_DESIGNWARE_ETH to Kconfig

Move this to Kconfig and clean up board config files that use it. Also
rename it to CONFIG_ETH_DESIGNWARE to fit with the naming that exists
in drivers/net/Kconfig.

Signed-off-by: Simon Glass <sjg@chromium.org>
Version 1:
Acked-by: Joe Hershberger <joe.hershberger@ni.com>
diff --git a/configs/Wits_Pro_A20_DKT_defconfig b/configs/Wits_Pro_A20_DKT_defconfig
index 9147ead..92c33b3 100644
--- a/configs/Wits_Pro_A20_DKT_defconfig
+++ b/configs/Wits_Pro_A20_DKT_defconfig
@@ -13,3 +13,6 @@
 CONFIG_DRAM_CLK=384
 CONFIG_DRAM_ZQ=127
 CONFIG_DRAM_EMR1=4
+CONFIG_ETH_DESIGNWARE=y
+CONFIG_NETDEVICES=y
+CONFIG_NET=y