spl: Kconfig: Rename SPL_USBETH_SUPPORT to SPL_USB_ETHER to match with the U-boot CONFIG

Rename CONFIG_SPL_USBETH_SUPPORT to CONFIG_SPL_USB_ETHER.

This enables users to block text using CONFIG_IS_ENABLED() instead
of resorting to #if ladders with SPL and non-SPL cases.

Signed-off-by: Faiz Abbas <faiz_abbas@ti.com>
diff --git a/board/vscom/baltos/board.c b/board/vscom/baltos/board.c
index cb39190..533d45e 100644
--- a/board/vscom/baltos/board.c
+++ b/board/vscom/baltos/board.c
@@ -423,7 +423,7 @@
 };
 #endif
 
-#if ((defined(CONFIG_SPL_ETH_SUPPORT) || defined(CONFIG_SPL_USBETH_SUPPORT)) \
+#if ((defined(CONFIG_SPL_ETH_SUPPORT) || defined(CONFIG_SPL_USB_ETHER)) \
 		&& defined(CONFIG_SPL_BUILD)) || \
 	((defined(CONFIG_DRIVER_TI_CPSW) || \
 	  defined(CONFIG_USB_ETHER) && defined(CONFIG_USB_MUSB_GADGET)) && \