sh: add common dram_init() function for all boards

Generic board support assumes a different method of specifying
DRAM size on board, also it can be shared among all boards, notably
only sh7763rdp board has a custom legacy dram_init(), however
the difference is only in printing some additional information,
this feature can be removed.

Signed-off-by: Vladimir Zapolskiy <vz@mleia.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

arch/sh/lib/board.c

@@ -0,0 +1,17 @@
+/*
+ * Copyright (C) 2016 Vladimir Zapolskiy <vz@mleia.com>
+ *
+ * SPDX-License-Identifier:     GPL-2.0+
+ */
+
+#include <common.h>
+
+DECLARE_GLOBAL_DATA_PTR;
+
+int dram_init(void)
+{
+	gd->ram_size = get_ram_size((long *)CONFIG_SYS_SDRAM_BASE,
+				    CONFIG_SYS_SDRAM_SIZE);
+
+	return 0;
+}