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/Linksprite_pcDuino3_Nano_defconfig b/configs/Linksprite_pcDuino3_Nano_defconfig
index 15a883a..9d171bd 100644
--- a/configs/Linksprite_pcDuino3_Nano_defconfig
+++ b/configs/Linksprite_pcDuino3_Nano_defconfig
@@ -9,3 +9,6 @@
 CONFIG_DRAM_CLK=408
 CONFIG_DRAM_ZQ=122
 CONFIG_DRAM_EMR1=4
+CONFIG_ETH_DESIGNWARE=y
+CONFIG_NETDEVICES=y
+CONFIG_NET=y