net: mediatek: add support for SGMII 1Gbps auto-negotiation mode

Existing SGMII support of mtk-eth is actually a MediaTek-specific
2.5Gbps high-speed SGMII (HSGMII) which does not support
auto-negotiation mode.

This patch adds SGMII 1Gbps auto-negotiation mode and rename the
existing HSGMII to 2500basex.

diff --git a/drivers/net/mtk_eth.h b/drivers/net/mtk_eth.h
index 1382ccb..320266c 100644
--- a/drivers/net/mtk_eth.h
+++ b/drivers/net/mtk_eth.h
@@ -69,6 +69,7 @@
 #define SGMII_AN_RESTART		BIT(9)
 
 #define SGMSYS_SGMII_MODE		0x20
+#define SGMII_AN_MODE			0x31120103
 #define SGMII_FORCE_MODE		0x31120019
 
 #define SGMSYS_QPHY_PWR_STATE_CTRL	0xe8
@@ -168,6 +169,7 @@
 #define FORCE_MODE			BIT(15)
 #define MAC_TX_EN			BIT(14)
 #define MAC_RX_EN			BIT(13)
+#define DEL_RXFIFO_CLR			BIT(12)
 #define BKOFF_EN			BIT(9)
 #define BACKPR_EN			BIT(8)
 #define FORCE_RX_FC			BIT(5)