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/MPC8536DS_SPIFLASH_defconfig b/configs/MPC8536DS_SPIFLASH_defconfig
index 0453cd2..ad0ae69 100644
--- a/configs/MPC8536DS_SPIFLASH_defconfig
+++ b/configs/MPC8536DS_SPIFLASH_defconfig
@@ -3,3 +3,5 @@
 CONFIG_TARGET_MPC8536DS=y
 CONFIG_SYS_EXTRA_OPTIONS="SPIFLASH"
 CONFIG_SPI_FLASH=y
+CONFIG_NETDEVICES=y
+CONFIG_E1000=y