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/axs103_defconfig b/configs/axs103_defconfig
index 7d662ad..e92fd7c 100644
--- a/configs/axs103_defconfig
+++ b/configs/axs103_defconfig
@@ -3,3 +3,6 @@
 CONFIG_TARGET_AXS101=y
 CONFIG_SYS_TEXT_BASE=0x81000000
 CONFIG_SYS_CLK_FREQ=50000000
+CONFIG_ETH_DESIGNWARE=y
+CONFIG_NETDEVICES=y
+CONFIG_NET=y