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/P1020MBG-PC_defconfig b/configs/P1020MBG-PC_defconfig
index 905b94c..bc408b7 100644
--- a/configs/P1020MBG-PC_defconfig
+++ b/configs/P1020MBG-PC_defconfig
@@ -2,3 +2,5 @@
 CONFIG_MPC85xx=y
 CONFIG_TARGET_P1_P2_RDB_PC=y
 CONFIG_SYS_EXTRA_OPTIONS="P1020MBG"
+CONFIG_NETDEVICES=y
+CONFIG_E1000=y