common: Move dram_init() declaration to common location

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

arch/sandbox/include/asm/u-boot-sandbox.h

@@ -17,7 +17,6 @@
 
 /* board/.../... */
 int board_init(void);
-int dram_init(void);
 
 /* start.c */
 int sandbox_early_getopt_check(void);