net: Move CONFIG_E1000 options to Kconfig

Move config for the E1000 Ethernet driver to Kconfig and tidy up affected
boards.

Signed-off-by: Simon Glass <sjg@chromium.org>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>
diff --git a/configs/B4420QDS_SPIFLASH_defconfig b/configs/B4420QDS_SPIFLASH_defconfig
index 6352ef9..5c6a319 100644
--- a/configs/B4420QDS_SPIFLASH_defconfig
+++ b/configs/B4420QDS_SPIFLASH_defconfig
@@ -3,3 +3,5 @@
 CONFIG_TARGET_B4860QDS=y
 CONFIG_SYS_EXTRA_OPTIONS="PPC_B4420,RAMBOOT_PBL,SPIFLASH,SYS_TEXT_BASE=0xFFF40000"
 CONFIG_SPI_FLASH=y
+CONFIG_NETDEVICES=y
+CONFIG_E1000=y