dm: phy: add missing #ifdef CONFIG_PHY

To avoid compilation breakage on platform that doesn't
support DM PHY but uses xhci-dwc3 driver, add the missing
CONFIG_PHY flag.

Introduced by patch :
84e53877 "usb: host: xhci-dwc3: Add generic PHY support"

Cc: Ran Wang <ran.wang_1@nxp.com>
Cc: Bin Meng <bmeng.cn@gmail.com>

Signed-off-by: Patrice Chotard <patrice.chotard@st.com>
Reported-by: Ran Wang <ran.wang_1@nxp.com>

include/generic-phy.h

@@ -122,6 +122,7 @@ struct phy_ops {
 	int	(*power_off)(struct phy *phy);
 };
 
+#ifdef CONFIG_PHY
 
 /**
  * generic_phy_init() - initialize the PHY port
@@ -220,6 +221,47 @@ int generic_phy_get_by_index(struct udevice *user, int index,
 int generic_phy_get_by_name(struct udevice *user, const char *phy_name,
 			    struct phy *phy);
 
+#else /* CONFIG_PHY */
+
+static inline int generic_phy_init(struct phy *phy)
+{
+	return 0;
+}
+
+static inline int generic_phy_exit(struct phy *phy)
+{
+	return 0;
+}
+
+static inline int generic_phy_reset(struct phy *phy)
+{
+	return 0;
+}
+
+static inline int generic_phy_power_on(struct phy *phy)
+{
+	return 0;
+}
+
+static inline int generic_phy_power_off(struct phy *phy)
+{
+	return 0;
+}
+
+static inline int generic_phy_get_by_index(struct udevice *user, int index,
+			     struct phy *phy)
+{
+	return 0;
+}
+
+static inline int generic_phy_get_by_name(struct udevice *user, const char *phy_name,
+			    struct phy *phy)
+{
+	return 0;
+}
+
+#endif /* CONFIG_PHY */
+
 /**
  * generic_phy_valid() - check if PHY port is valid
  *