net: ethernet: ti: am65-cpsw-nuss: enable 10Mbps link speed in rgmii mode

In RGMII mode the 10Mbps link speed is supported only when CPSW2G MAC SL is
configured for External Control ("in band") mode
CPSW_PN_MAC_CONTROL_REG.CTL_EN(18) = 1

Hence update am65_cpsw_update_link() to follow documentation.

Signed-off-by: Murali Karicheri <m-karicheri2@ti.com>
Reviewed-by: Grygorii Strashko <grygorii.strashko@ti.com>
diff --git a/drivers/net/ti/am65-cpsw-nuss.c b/drivers/net/ti/am65-cpsw-nuss.c
index 2b77213..7531a07 100644
--- a/drivers/net/ti/am65-cpsw-nuss.c
+++ b/drivers/net/ti/am65-cpsw-nuss.c
@@ -61,6 +61,7 @@
 
 #define AM65_CPSW_MACSL_CTL_REG			0x0
 #define AM65_CPSW_MACSL_CTL_REG_IFCTL_A		BIT(15)
+#define AM65_CPSW_MACSL_CTL_EXT_EN		BIT(18)
 #define AM65_CPSW_MACSL_CTL_REG_GIG		BIT(7)
 #define AM65_CPSW_MACSL_CTL_REG_GMII_EN		BIT(5)
 #define AM65_CPSW_MACSL_CTL_REG_LOOPBACK	BIT(1)
@@ -187,6 +188,9 @@
 			      AM65_CPSW_MACSL_CTL_REG_GMII_EN;
 		if (phy->speed == 1000)
 			mac_control |= AM65_CPSW_MACSL_CTL_REG_GIG;
+		if (phy->speed == 10 && phy_interface_is_rgmii(phy))
+			/* Can be used with in band mode only */
+			mac_control |= AM65_CPSW_MACSL_CTL_EXT_EN;
 		if (phy->duplex == DUPLEX_FULL)
 			mac_control |= AM65_CPSW_MACSL_CTL_REG_FULL_DUPLEX;
 		if (phy->speed == 100)