arm: socfpga: spl: Add stub sdram.h

Since the SoCFPGA SDRAM support is not yet applied to u-boot, we still
need to be able to compile the codebase. Introduce stub functions which
temporarily supplement the missing SDRAM setup functions.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Chin Liang See <clsee@opensource.altera.com>
Cc: Dinh Nguyen <dinguyen@opensource.altera.com>
Cc: Pavel Machek <pavel@denx.de>
Cc: Stefan Roese <sr@denx.de>
Cc: Tom Rini <trini@konsulko.com>
Cc: Vince Bridgers <vbridger@opensource.altera.com>

arch/arm/include/asm/arch-socfpga/sdram.h

@@ -0,0 +1,19 @@
+/*
+ * Copyright (C) 2015 Marek Vasut <marex@denx.de>
+ *
+ * FIXME: This file contains temporary stub functions and is here
+ *        only until these functions are properly merged into
+ *        mainline.
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#ifndef __ARCH_SDRAM_H__
+#define __ARCH_SDRAM_H__
+
+/* function declaration */
+inline unsigned long sdram_calculate_size(void) { return 0; }
+inline unsigned sdram_mmr_init_full(unsigned int sdr_phy_reg) { return 0; }
+inline int sdram_calibration_full(void) { return 0; }
+
+#endif	/* __ARCH_SDRAM_H__ */