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/Cubieboard2_defconfig b/configs/Cubieboard2_defconfig
index d866ad1..7f65c1d 100644
--- a/configs/Cubieboard2_defconfig
+++ b/configs/Cubieboard2_defconfig
@@ -8,3 +8,6 @@
 CONFIG_DRAM_CLK=480
 CONFIG_DRAM_ZQ=127
 CONFIG_DRAM_EMR1=4
+CONFIG_ETH_DESIGNWARE=y
+CONFIG_NETDEVICES=y
+CONFIG_NET=y