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/Kconfig b/drivers/net/Kconfig
index 5bd66ea..973258a 100644
--- a/drivers/net/Kconfig
+++ b/drivers/net/Kconfig
@@ -39,4 +39,11 @@
 	  network traffic to be tested from within sandbox. See
 	  board/sandbox/README.sandbox for more details.
 
+config ETH_DESIGNWARE
+	bool "Synopsys Designware Ethernet MAC"
+	help
+	  This MAC is present in SoCs from various vendors. It supports
+	  100Mbit and 1 Gbit operation. You must enable CONFIG_PHYLIB to
+	  provide the PHY (physical media interface).
+
 endif # NETDEVICES