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/MPC8572DS_defconfig b/configs/MPC8572DS_defconfig
index dde9eb2..2f69b14 100644
--- a/configs/MPC8572DS_defconfig
+++ b/configs/MPC8572DS_defconfig
@@ -1,3 +1,5 @@
 CONFIG_PPC=y
 CONFIG_MPC85xx=y
 CONFIG_TARGET_MPC8572DS=y
+CONFIG_NETDEVICES=y
+CONFIG_E1000=y