common: Move board_get_usable_ram_top() out of common.h

Move this function into init.h which seems to be designed for this sort
of thing. Also update the header to declare struct global_data so that it
can be included without global_data.h being needed.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@konsulko.com>

board/armadeus/apf27/apf27.c

@@ -7,6 +7,7 @@
  */
 
 #include <common.h>
+#include <init.h>
 #include <jffs2/jffs2.h>
 #include <nand.h>
 #include <netdev.h>

board/imgtec/boston/ddr.c

@@ -4,6 +4,7 @@
  */
 
 #include <common.h>
+#include <init.h>
 
 #include <asm/io.h>
 

board/menlo/m53menlo/m53menlo.c

@@ -8,6 +8,7 @@
 
 #include <common.h>
 #include <dm.h>
+#include <init.h>
 #include <asm/io.h>
 #include <asm/arch/imx-regs.h>
 #include <asm/arch/sys_proto.h>

board/raspberrypi/rpi/rpi.c

@@ -10,6 +10,7 @@
 #include <efi_loader.h>
 #include <fdt_support.h>
 #include <fdt_simplefb.h>
+#include <init.h>
 #include <lcd.h>
 #include <memalign.h>
 #include <mmc.h>

board/ti/am65x/evm.c

@@ -9,6 +9,7 @@
 
 #include <common.h>
 #include <dm.h>
+#include <init.h>
 #include <asm/arch/sys_proto.h>
 #include <asm/arch/hardware.h>
 #include <asm/gpio.h>

board/ti/j721e/evm.c

@@ -8,6 +8,7 @@
  */
 
 #include <common.h>
+#include <init.h>
 #include <asm/io.h>
 #include <spl.h>
 #include <asm/arch/sys_proto.h>