net: dm: fec: Support the phy-supply binding

Configure the phy regulator if defined by the "phy-supply" DT phandle.

Signed-off-by: Martin Fuzzey <martin.fuzzey@flowbird.group>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>
diff --git a/drivers/net/fec_mxc.h b/drivers/net/fec_mxc.h
index fd89443..848cd7c 100644
--- a/drivers/net/fec_mxc.h
+++ b/drivers/net/fec_mxc.h
@@ -250,6 +250,9 @@
 	int phy_id;
 	int (*mii_postcall)(int);
 #endif
+#ifdef CONFIG_DM_REGULATOR
+	struct udevice *phy_supply;
+#endif
 #ifdef CONFIG_DM_GPIO
 	struct gpio_desc phy_reset_gpio;
 	uint32_t reset_delay;