Copyright: Move to SPDX-Identifier

SPDX-Identifier cleans up the files and creates visibility on each file
while not using too much space.

Replacing all instances on the long apache-2.0 text and adding the
SPDX-Identifier where not present before.

Change-Id: I7566febfd29dac6c81df6ff4045a6663aa50fca4
Signed-off-by: Christopher Meis <christopher.meis@9elements.com>
Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
diff --git a/gpioMon.hpp b/gpioMon.hpp
index 2add08c..2d68891 100644
--- a/gpioMon.hpp
+++ b/gpioMon.hpp
@@ -1,3 +1,6 @@
+// SPDX-License-Identifier: Apache-2.0
+// SPDX-FileCopyrightText: Copyright OpenBMC Authors
+
 #pragma once
 
 #include <gpiod.h>