net: dwc_eth_xgmac_socfpga: Add support for rgmii-id mode.

An issue was identified where selecting the phy-mode as
rgmii-id in the device tree source (DTS) would cause the
`dwc_eth_xgmac_socfpga` driver to raise an unsupported phy mode error.

From the MAC controller's perspective, the rgmii and rgmii-id
phy modes are effectively identical. To address this, both
modes will now be configured to rgmii in the MAC controller.

This change ensures that the rgmii-id phy mode is properly
supported without error.

Signed-off-by: Boon Khai Ng <boon.khai.ng@intel.com>
Reviewed-by: Tien Fong Chee <tien.fong.chee@intel.com>
diff --git a/drivers/net/dwc_eth_xgmac_socfpga.c b/drivers/net/dwc_eth_xgmac_socfpga.c
index 87fb7e8..1864187 100644
--- a/drivers/net/dwc_eth_xgmac_socfpga.c
+++ b/drivers/net/dwc_eth_xgmac_socfpga.c
@@ -80,6 +80,7 @@
 		modereg = SYSMGR_EMACGRP_CTRL_PHYSEL_ENUM_RMII;
 		break;
 	case PHY_INTERFACE_MODE_RGMII:
+	case PHY_INTERFACE_MODE_RGMII_ID:
 		modereg = SYSMGR_EMACGRP_CTRL_PHYSEL_ENUM_RGMII;
 		break;
 	default: