plat/sgi: refactor SDEI specific macros

The macros specific to SDEI defined in the sgi_base_platform_def.h are
not applicable for all the platforms supported by plat/sgi. So refactor
the SDEI specific macros into a new header file and include this file on
only on platforms it is applicable on.

Signed-off-by: Thomas Abraham <thomas.abraham@arm.com>
Change-Id: I0cb7125334f02a21cae1837cdfd765c16ab50bf5
diff --git a/plat/arm/board/rde1edge/include/platform_def.h b/plat/arm/board/rde1edge/include/platform_def.h
index c39fe2b..a9b30a4 100644
--- a/plat/arm/board/rde1edge/include/platform_def.h
+++ b/plat/arm/board/rde1edge/include/platform_def.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2018-2020, Arm Limited. All rights reserved.
+ * Copyright (c) 2018-2021, Arm Limited. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -9,6 +9,7 @@
 
 #include <lib/utils_def.h>
 
+#include <sgi_sdei.h>
 #include <sgi_soc_platform_def.h>
 
 #define PLAT_ARM_CLUSTER_COUNT		U(2)