Rename SPL_ETH_SUPPORT to SPL_ETH

Rename this option so that CONFIG_IS_ENABLED can be used with it.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/doc/SPL/README.am335x-network b/doc/SPL/README.am335x-network
index e3cf93f..e052706 100644
--- a/doc/SPL/README.am335x-network
+++ b/doc/SPL/README.am335x-network
@@ -8,7 +8,7 @@
  I. Building the required images
   1. You have to enable generic SPL configuration options (see
 doc/README.SPL) as well as CONFIG_SPL_NET_SUPPORT,
-CONFIG_ETH_SUPPORT, CONFIG_SPL_LIBGENERIC_SUPPORT and
+CONFIG_SPL_ETH, CONFIG_SPL_LIBGENERIC_SUPPORT and
 CONFIG_SPL_LIBCOMMON_SUPPORT in your board configuration file to build
 SPL with support for booting over the network. Also you have to enable
 the driver for the NIC used and CONFIG_SPL_BOARD_INIT option if your