xtensa: xtfpga: only select ethoc when ethernet is available

Otherwise we get the following build warning:
    (XTENSA_PLATFORM_XTFPGA) selects ETHOC which has unmet direct
    dependencies (NETDEVICES && ETHERNET && HAS_IOMEM && HAS_DMA)

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
diff --git a/arch/xtensa/Kconfig b/arch/xtensa/Kconfig
index 390bafe..81f57e8 100644
--- a/arch/xtensa/Kconfig
+++ b/arch/xtensa/Kconfig
@@ -319,8 +319,8 @@
 
 config XTENSA_PLATFORM_XTFPGA
 	bool "XTFPGA"
+	select ETHOC if ETHERNET
 	select SERIAL_CONSOLE
-	select ETHOC
 	select XTENSA_CALIBRATE_CCOUNT
 	help
 	  XTFPGA is the name of Tensilica board family (LX60, LX110, LX200, ML605).