phy: Add helper function to check phy interface mode

Added helper function that checks phy_mode is RGMII (all variants)
'bool phy_interface_mode_is_rgmii(phy_interface_t mode)'

Changed the following function, to use the above.
'bool phy_interface_is_rgmii(struct phy_device *phydev)'
Signed-off-by: Iyappan Subramanian <isubramanian@apm.com>
Suggested-by: Florian Fainelli <f.fainelli@gmail.com>
Suggested-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/phy.h

@@ -715,6 +715,17 @@ static inline bool phy_is_internal(struct phy_device *phydev)
 	return phydev->is_internal;
 }
 
+/**
+ * phy_interface_mode_is_rgmii - Convenience function for testing if a
+ * PHY interface mode is RGMII (all variants)
+ * @mode: the phy_interface_t enum
+ */
+static inline bool phy_interface_mode_is_rgmii(phy_interface_t mode)
+{
+	return mode >= PHY_INTERFACE_MODE_RGMII &&
+		mode <= PHY_INTERFACE_MODE_RGMII_TXID;
+};
+
 /**
  * phy_interface_is_rgmii - Convenience function for testing if a PHY interface
  * is RGMII (all variants)
@@ -722,8 +733,7 @@ static inline bool phy_is_internal(struct phy_device *phydev)
  */
 static inline bool phy_interface_is_rgmii(struct phy_device *phydev)
 {
-	return phydev->interface >= PHY_INTERFACE_MODE_RGMII &&
-		phydev->interface <= PHY_INTERFACE_MODE_RGMII_TXID;
+	return phy_interface_mode_is_rgmii(phydev->interface);
 };
 
 /*