net: phy: mdio-gpio: Add #defines for the GPIO index's

The GPIOs are described in device tree using a list, without names.
Add defines to indicate what each index in the list means. These
defines should also be used by platform devices passing GPIOs via a
GPIO lookup table.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/linux/mdio-gpio.h b/include/linux/mdio-gpio.h
new file mode 100644
index 0000000..cea443a6
--- /dev/null
+++ b/include/linux/mdio-gpio.h
@@ -0,0 +1,9 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __LINUX_MDIO_GPIO_H
+#define __LINUX_MDIO_GPIO_H
+
+#define MDIO_GPIO_MDC	0
+#define MDIO_GPIO_MDIO	1
+#define MDIO_GPIO_MDO	2
+
+#endif