net: add Kconfig for MVGBE

Add Kconfig for MVGBE and update boards to select this.

Signed-off-by: Chris Packham <judge.packham@gmail.com>
Reviewed-by: Stefan Roese <sr@denx.de>
diff --git a/configs/dreamplug_defconfig b/configs/dreamplug_defconfig
index 17c53a3..cbd2fb6 100644
--- a/configs/dreamplug_defconfig
+++ b/configs/dreamplug_defconfig
@@ -24,6 +24,8 @@
 # CONFIG_MMC is not set
 CONFIG_SPI_FLASH=y
 CONFIG_SPI_FLASH_MACRONIX=y
+CONFIG_NETDEVICES=y
+CONFIG_MVGBE=y
 CONFIG_SYS_NS16550=y
 CONFIG_SPI=y
 CONFIG_KIRKWOOD_SPI=y