net: mediatek: make sgmii/usxgmii optional

Not all platforms supports sgmii and/or usxgmii. So we add Kconfig
options for these features and enable them only for supported
platforms.

diff --git a/drivers/net/Kconfig b/drivers/net/Kconfig
index 576cd2d..5a57d05 100644
--- a/drivers/net/Kconfig
+++ b/drivers/net/Kconfig
@@ -975,6 +975,18 @@
 	  This Driver support MediaTek Ethernet GMAC
 	  Say Y to enable support for the MediaTek Ethernet GMAC.
 
+if MEDIATEK_ETH
+
+config MTK_ETH_SGMII
+	bool
+	default y if ARCH_MEDIATEK && !TARGET_MT7623
+
+config MTK_ETH_XGMII
+	bool
+	default y if TARGET_MT7987 || TARGET_MT7988
+
+endif # MEDIATEK_ETH
+
 config HIFEMAC_ETH
 	bool "HiSilicon Fast Ethernet Controller"
 	select DM_CLK