soc/sifive: move ram_resource to mainboard

ram_resource is board specific and should be moved there.

Change-Id: I50bd9aaaae39422e565d8bf205a6365c59299df0
Signed-off-by: Philipp Hug <philipp@hug.cx>
Reviewed-on: https://review.coreboot.org/28621
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>

src/mainboard/sifive/hifive-unleashed/mainboard.c

@@ -13,12 +13,14 @@
  * GNU General Public License for more details.
  */
 
-#include <device/device.h>
-#include <bootblock_common.h>
-#include <timestamp.h>
+#include <arch/io.h>
+#include <console/console.h>
+#include <soc/sdram.h>
+#include <symbols.h>
 
 static void mainboard_enable(struct device *dev)
 {
+	ram_resource(dev, 0, (uintptr_t)_dram/KiB, sdram_size_mb()*KiB);
 }
 
 struct chip_operations mainboard_ops = {