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/P5020DS_NAND_defconfig b/configs/P5020DS_NAND_defconfig
index a071029..64ba6e9 100644
--- a/configs/P5020DS_NAND_defconfig
+++ b/configs/P5020DS_NAND_defconfig
@@ -3,3 +3,5 @@
 CONFIG_TARGET_P5020DS=y
 CONFIG_SYS_EXTRA_OPTIONS="RAMBOOT_PBL,NAND,SYS_TEXT_BASE=0xFFF40000"
 CONFIG_SPI_FLASH=y
+CONFIG_NETDEVICES=y
+CONFIG_E1000=y