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/css/sgi/include/sgi_sdei.h b/plat/arm/css/sgi/include/sgi_sdei.h
new file mode 100644
index 0000000..f380122
--- /dev/null
+++ b/plat/arm/css/sgi/include/sgi_sdei.h
@@ -0,0 +1,25 @@
+/*
+ * Copyright (c) 2021, ARM Limited and Contributors. All rights reserved.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#ifndef SGI_SDEI_H
+#define SGI_SDEI_H
+
+#if SDEI_SUPPORT
+
+/* ARM SDEI dynamic shared event numbers */
+#define SGI_SDEI_DS_EVENT_0		U(804)
+#define SGI_SDEI_DS_EVENT_1		U(805)
+
+#define PLAT_ARM_PRIVATE_SDEI_EVENTS					      \
+		SDEI_DEFINE_EVENT_0(ARM_SDEI_SGI),			      \
+		SDEI_EXPLICIT_EVENT(SGI_SDEI_DS_EVENT_0, SDEI_MAPF_CRITICAL), \
+		SDEI_EXPLICIT_EVENT(SGI_SDEI_DS_EVENT_1, SDEI_MAPF_CRITICAL),
+
+#define PLAT_ARM_SHARED_SDEI_EVENTS
+
+#endif /* SDEI_SUPPORT */
+
+#endif /* SGI_SDEI_H */