net: Move the CMD_NET config to defconfigs

This also selects CONFIG_NET for any CONFIG_CMD_NET board.

Remove the imx default for CONFIG_NET.

This moves the config that was defined by 60296a8 (commands: add more
command entries in Kconfig).

Signed-off-by: Joe Hershberger <joe.hershberger@ni.com>
diff --git a/configs/P1010RDB-PA_36BIT_NOR_defconfig b/configs/P1010RDB-PA_36BIT_NOR_defconfig
index cf4718d..2e7d281 100644
--- a/configs/P1010RDB-PA_36BIT_NOR_defconfig
+++ b/configs/P1010RDB-PA_36BIT_NOR_defconfig
@@ -3,3 +3,4 @@
 CONFIG_TARGET_P1010RDB=y
 CONFIG_SYS_EXTRA_OPTIONS="P1010RDB_PA,36BIT"
 CONFIG_CMD_SETEXPR=y
+CONFIG_CMD_NET=y