net: phy: DP83822: enable rgmii mode if phy_interface_is_rgmii

RGMII mode can be enable from dp83822 straps, and also writing bit 9
of register 0x17 - RMII and Status Register (RCSR).
When phy_interface_is_rgmii rgmii mode must be enabled, same for
contrary, this prevents malconfigurations of hw straps

References:
 - https://www.ti.com/lit/gpn/dp83822i p66

Signed-off-by: Tommaso Merciai <tommaso.merciai@amarulasolutions.com>
Co-developed-by: Michael Trimarchi <michael@amarulasolutions.com>
Suggested-by: Alberto Bianchi <alberto.bianchi@amarulasolutions.com>
Tested-by: Tommaso Merciai <tommaso.merciai@amarulasolutions.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/phy/dp83822.c

@@ -94,7 +94,8 @@
 #define DP83822_WOL_INDICATION_SEL BIT(8)
 #define DP83822_WOL_CLR_INDICATION BIT(11)
 
-/* RSCR bits */
+/* RCSR bits */
+#define DP83822_RGMII_MODE_EN	BIT(9)
 #define DP83822_RX_CLK_SHIFT	BIT(12)
 #define DP83822_TX_CLK_SHIFT	BIT(11)
 
@@ -408,6 +409,12 @@ static int dp83822_config_init(struct phy_device *phydev)
 			if (err)
 				return err;
 		}
+
+		phy_set_bits_mmd(phydev, DP83822_DEVADDR,
+					MII_DP83822_RCSR, DP83822_RGMII_MODE_EN);
+	} else {
+		phy_clear_bits_mmd(phydev, DP83822_DEVADDR,
+					MII_DP83822_RCSR, DP83822_RGMII_MODE_EN);
 	}
 
 	if (dp83822->fx_enabled) {