license: add spdx identifier to all files

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: Ifddd07cc0eb5edeb2dcb410747073d68c6631cb1
diff --git a/include/libpldm/entity.h b/include/libpldm/entity.h
index 9e657c1..ab2c175 100644
--- a/include/libpldm/entity.h
+++ b/include/libpldm/entity.h
@@ -1,3 +1,4 @@
+/* SPDX-License-Identifier: Apache-2.0 OR GPL-2.0-or-later */
 #ifndef ENTITY_H
 #define ENTITY_H