arm: Add arm handoff header file

Add an arch-specific handoff header so that we can use the HANDOFF feature
on arm devices.

Signed-off-by: Michael Trimarchi <michael@amarulasolutions.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

arch/arm/include/asm/handoff.h

@@ -0,0 +1,21 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * Architecture-specific SPL handoff information for ARM
+ *
+ * Copyright 2019 Amarula Solutions, BV
+ * Written by Michael Trimarchi <michael@amarulasolutions.com>
+ */
+
+#ifndef __asm_handoff_h
+#define __asm_handoff_h
+
+/**
+ * struct arch_spl_handoff - architecture-specific handoff info
+ *
+ * @usable_ram_top: Value returned by board_get_usable_ram_top() in SPL
+ */
+struct arch_spl_handoff {
+	ulong usable_ram_top;
+};
+
+#endif