net: Rename SPL_NET_SUPPORT to SPL_NET

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

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/am335x_boneblack_vboot_defconfig b/configs/am335x_boneblack_vboot_defconfig
index f411d58..368d013 100644
--- a/configs/am335x_boneblack_vboot_defconfig
+++ b/configs/am335x_boneblack_vboot_defconfig
@@ -21,7 +21,7 @@
 CONFIG_ARCH_MISC_INIT=y
 CONFIG_SPL_MUSB_NEW=y
 # CONFIG_SPL_NAND_SUPPORT is not set
-CONFIG_SPL_NET_SUPPORT=y
+CONFIG_SPL_NET=y
 CONFIG_SPL_NET_VCI_STRING="AM33xx U-Boot SPL"
 CONFIG_SPL_OS_BOOT=y
 CONFIG_SPL_USB_GADGET=y