Merge changes from topic "pb/tbbr-oid" into integration

* changes:
  doc: Clarify cert_create build when USE_TBBR_DEFS=0
  plat/sgm: Remove redundant platform_oid.h

docs/user-guide.rst

@@ -1219,11 +1219,13 @@ command:
     make PLAT=<platform> [DEBUG=1] [V=1] certtool
 
 For platforms that require their own IDs in certificate files, the generic
-'cert_create' tool can be built with the following command:
+'cert_create' tool can be built with the following command. Note that the target
+platform must define its IDs within a ``platform_oid.h`` header file for the
+build to succeed.
 
 ::
 
-    make USE_TBBR_DEFS=0 [DEBUG=1] [V=1] certtool
+    make PLAT=<platform> USE_TBBR_DEFS=0 [DEBUG=1] [V=1] certtool
 
 ``DEBUG=1`` builds the tool in debug mode. ``V=1`` makes the build process more
 verbose. The following command should be used to obtain help about the tool:

plat/arm/css/sgm/include/platform_oid.h

@@ -1,12 +0,0 @@
-/*
- * Copyright (c) 2018, ARM Limited and Contributors. All rights reserved.
- *
- * SPDX-License-Identifier: BSD-3-Clause
- */
-
-#include <plat/arm/board/common/board_arm_oid.h>
-
-/*
- * Required platform OIDs
- * (Provided by included header)
- */