riscv: sifive: fu540: add SPL configuration

Add a support for SPL which will boot from L2 LIM (0x0800_0000) and
then SPL will boot U-Boot FIT image (OpenSBI FW_DYNAMIC + u-boot.bin)
from MMC boot devices.

SPL related code is leveraged from FSBL
(https://github.com/sifive/freedom-u540-c000-bootloader.git)

Signed-off-by: Pragnesh Patel <pragnesh.patel@sifive.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Tested-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Jagan Teki <jagan@amarulasolutions.com>
Tested-by: Jagan Teki <jagan@amarulasolutions.com>
diff --git a/arch/riscv/include/asm/arch-fu540/spl.h b/arch/riscv/include/asm/arch-fu540/spl.h
new file mode 100644
index 0000000..0c188be
--- /dev/null
+++ b/arch/riscv/include/asm/arch-fu540/spl.h
@@ -0,0 +1,14 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * Copyright (C) 2020 SiFive, Inc.
+ *
+ * Authors:
+ *   Pragnesh Patel <pragnesh.patel@sifve.com>
+ */
+
+#ifndef _SPL_SIFIVE_H
+#define _SPL_SIFIVE_H
+
+int soc_spl_init(void);
+
+#endif /* _SPL_SIFIVE_H */