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/arch/arm/mach-omap2/boot-common.c b/arch/arm/mach-omap2/boot-common.c
index 26245aa..db68a9d 100644
--- a/arch/arm/mach-omap2/boot-common.c
+++ b/arch/arm/mach-omap2/boot-common.c
@@ -99,7 +99,7 @@
 			sys_boot_device = 1;
 			break;
 #endif
-#if defined(BOOT_DEVICE_USBETH) && !defined(CONFIG_SPL_USBETH_SUPPORT)
+#if defined(BOOT_DEVICE_USBETH) && !defined(CONFIG_SPL_USB_ETHER)
 		case BOOT_DEVICE_USBETH:
 			sys_boot_device = 1;
 			break;