net: phy: Convert some PHY and MDIO driver files to SPDX headers

Where the license text and the MODULE_LICENSE() value agree, convert
to using an SPDX header, removing the license text.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/phy/mdio-boardinfo.c

@@ -1,10 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0+
 /*
  * mdio-boardinfo - Collect pre-declarations for MDIO devices
- *
- * This program is free software; you can redistribute  it and/or modify it
- * under  the terms of  the GNU General  Public License as published by the
- * Free Software Foundation;  either version 2 of the  License, or (at your
- * option) any later version.
  */
 
 #include <linux/kernel.h>