intel: add SPDX identifiers to all the Intel drivers

Add the SPDX identifiers to all the Intel wired LAN driver files, as
outlined in Documentation/process/license-rules.rst.

Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/ethernet/intel/igb/igb_ptp.c b/drivers/net/ethernet/intel/igb/igb_ptp.c
index 0746b19..7454b98 100644
--- a/drivers/net/ethernet/intel/igb/igb_ptp.c
+++ b/drivers/net/ethernet/intel/igb/igb_ptp.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0+
 /* PTP Hardware Clock (PHC) driver for the Intel 82576 and 82580
  *
  * Copyright (C) 2011 Richard Cochran <richardcochran@gmail.com>