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/drivers/net/Makefile b/drivers/net/Makefile
index 2f22151..f24443d 100644
--- a/drivers/net/Makefile
+++ b/drivers/net/Makefile
@@ -16,7 +16,7 @@
 obj-$(CONFIG_CALXEDA_XGMAC) += calxedaxgmac.o
 obj-$(CONFIG_CS8900) += cs8900.o
 obj-$(CONFIG_TULIP) += dc2114x.o
-obj-$(CONFIG_DESIGNWARE_ETH) += designware.o
+obj-$(CONFIG_ETH_DESIGNWARE) += designware.o
 obj-$(CONFIG_DRIVER_DM9000) += dm9000x.o
 obj-$(CONFIG_DNET) += dnet.o
 obj-$(CONFIG_E1000) += e1000.o