km/rgmii: port Ethernet interface of KM Kirkwood boards to driver model

Activate the driver model for the Ethernet interface (RGMII) in the KM
Kirkwood Kconfig file. Additionally, raise the auto negotiation timeout
to eight seconds as more time is required for those boards.

Signed-off-by: Pascal Linder <pascal.linder@edu.hefr.ch>
Signed-off-by: Holger Brunck <holger.brunck@ch.abb.com>
Signed-off-by: Stefan Roese <sr@denx.de>
diff --git a/board/keymile/km_arm/Kconfig b/board/keymile/km_arm/Kconfig
index 335a454..be6b162 100644
--- a/board/keymile/km_arm/Kconfig
+++ b/board/keymile/km_arm/Kconfig
@@ -42,6 +42,7 @@
 	def_bool y
 	select BOARD_LATE_INIT
 	select DM
+	select DM_ETH
 	select DM_SERIAL
 	select DM_SPI
 	select DM_SPI_FLASH