stm32mp1: save boot information in backup registers

This will be used by BL33 to get boot device and instance.

Signed-off-by: Yann Gautier <yann.gautier@st.com>
Signed-off-by: Mathieu Belou <mathieu.belou@st.com>
Signed-off-by: Lionel Debieve <lionel.debieve@st.com>
diff --git a/plat/st/stm32mp1/include/stm32mp1_context.h b/plat/st/stm32mp1/include/stm32mp1_context.h
new file mode 100644
index 0000000..fd08afc
--- /dev/null
+++ b/plat/st/stm32mp1/include/stm32mp1_context.h
@@ -0,0 +1,14 @@
+/*
+ * Copyright (c) 2017-2018, ARM Limited and Contributors. All rights reserved.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#ifndef __STM32MP1_CONTEXT_H__
+#define __STM32MP1_CONTEXT_H__
+
+#include <stdint.h>
+
+int stm32_save_boot_interface(uint32_t interface, uint32_t instance);
+
+#endif /* __STM32MP1_CONTEXT_H__ */