net/ethoc: add Kconfig entry for the driver

Add Kconfig entry for the driver, remove #define CONFIG_ETHOC from the
only board configuration that uses it and put it into that board's
defconfig.

Cc: Stefan Kristiansson <stefan.kristiansson@saunalahti.fi>
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>
diff --git a/drivers/net/Kconfig b/drivers/net/Kconfig
index 88d8e83..be3ed73 100644
--- a/drivers/net/Kconfig
+++ b/drivers/net/Kconfig
@@ -124,6 +124,11 @@
 	  100Mbit and 1 Gbit operation. You must enable CONFIG_PHYLIB to
 	  provide the PHY (physical media interface).
 
+config ETHOC
+	bool "OpenCores 10/100 Mbps Ethernet MAC"
+	help
+	  This MAC is present in OpenRISC and Xtensa XTFPGA boards.
+
 config MVPP2
 	bool "Marvell Armada 375 network interface support"
 	depends on ARMADA_375