net: mdio: mux-meson-gxl: set reversed bit when using internal phy

This bit is necessary to receive packets from the internal PHY.
Without this bit set, no activity occurs on the interface.

Normally u-boot sets this bit, but if u-boot is compiled without
net support, the interface will be up but without any activity.
If bit is set once, it will work until the IP is powered down or reset.

The vendor SDK sets this bit along with the PHY_ID bits.

Signed-off-by: Da Xue <da@libre.computer>
Fixes: 9a24e1f ("net: mdio: add amlogic gxl mdio mux support")
Link: https://patch.msgid.link/20250425192009.1439508-1-da@libre.computer
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: Da Xue

drivers/net/mdio/mdio-mux-meson-gxl.c

@@ -17,6 +17,7 @@
 #define  REG2_LEDACT		GENMASK(23, 22)
 #define  REG2_LEDLINK		GENMASK(25, 24)
 #define  REG2_DIV4SEL		BIT(27)
+#define  REG2_REVERSED		BIT(28)
 #define  REG2_ADCBYPASS		BIT(30)
 #define  REG2_CLKINSEL		BIT(31)
 #define ETH_REG3		0x4
@@ -65,7 +66,7 @@ static void gxl_enable_internal_mdio(struct gxl_mdio_mux *priv)
 	 * The only constraint is that it must match the one in
 	 * drivers/net/phy/meson-gxl.c to properly match the PHY.
 	 */
-	writel(FIELD_PREP(REG2_PHYID, EPHY_GXL_ID),
+	writel(REG2_REVERSED | FIELD_PREP(REG2_PHYID, EPHY_GXL_ID),
 	       priv->regs + ETH_REG2);
 
 	/* Enable the internal phy */