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/spear600_usbtty_defconfig b/configs/spear600_usbtty_defconfig
index cf8b0ec..1e28edf 100644
--- a/configs/spear600_usbtty_defconfig
+++ b/configs/spear600_usbtty_defconfig
@@ -1,3 +1,6 @@
 CONFIG_SYS_EXTRA_OPTIONS="spear600,usbtty"
 CONFIG_ARM=y
 CONFIG_TARGET_SPEAR600=y
+CONFIG_ETH_DESIGNWARE=y
+CONFIG_NETDEVICES=y
+CONFIG_NET=y