net: gem: Disable PCS autonegotiation in case of fixed-link

Disable PCS autonegotiation if fixed-link node is present in device tree.
This way systems with multiple GEM instances with a combination of
SGMII-fixed and SGMII-PHY will work.
Reported-by: NGoran Marinkovic <goran.marinkovic@psi.ch>
Signed-off-by: NMichal Simek <michal.simek@xilinx.com>
Signed-off-by: NAshok Reddy Soma <ashok.reddy.soma@xilinx.com>
Signed-off-by: NMichal Simek <michal.simek@xilinx.com>

drivers/net/zynq_gem.c

@@ -451,8 +451,12 @@ static int zynq_gem_init(struct udevice *dev)
 		nwconfig |= ZYNQ_GEM_NWCFG_SGMII_ENBL |
 			    ZYNQ_GEM_NWCFG_PCS_SEL;
 #ifdef CONFIG_ARM64
+	if (priv->phydev->phy_id != PHY_FIXED_ID)
 		writel(readl(&regs->pcscntrl) | ZYNQ_GEM_PCS_CTL_ANEG_ENBL,
 		       &regs->pcscntrl);
+	else
+		writel(readl(&regs->pcscntrl) & ~ZYNQ_GEM_PCS_CTL_ANEG_ENBL,
+		       &regs->pcscntrl);
 #endif
 	}