rockchip: Print a message when returning to the bootrom

At present if the return to bootrom fails (e.g. because you are not using
the Rockchip's bootrom's pointer table in MMC) then the board prints
SPL message and hangs. Print a message first if we can, to help in
understanding what happened when it hangs.

Signed-off-by: Simon Glass <sjg@chromium.org>
Tested-by: Heiko Stuebner <heiko@sntech.de>
Acked-by: Heiko Stuebner <heiko@sntech.de>
diff --git a/arch/arm/mach-rockchip/bootrom.c b/arch/arm/mach-rockchip/bootrom.c
new file mode 100644
index 0000000..da36f92
--- /dev/null
+++ b/arch/arm/mach-rockchip/bootrom.c
@@ -0,0 +1,16 @@
+/**
+ * Copyright (c) 2017 Google, Inc
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#include <common.h>
+#include <asm/arch/bootrom.h>
+
+void back_to_bootrom(void)
+{
+#if defined(CONFIG_SPL_LIBGENERIC_SUPPORT) && !defined(CONFIG_TPL_BUILD)
+	printf("Returning to boot ROM...");
+#endif
+	_back_to_bootrom_s();
+}