monitor: Use the IEC binary prefix definitions

It eases code review, unit is explicit.

Patch generated using:

  $ git grep -n '[<>][<>]= ?[1-5]0'

and modified manually.
Suggested-by: NEric Blake <eblake@redhat.com>
Signed-off-by: NPhilippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20180625124238.25339-43-f4bug@amsat.org>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

monitor.c

@@ -23,6 +23,7 @@
  */
 
 #include "qemu/osdep.h"
+#include "qemu/units.h"
 #include <dirent.h>
 #include "cpu.h"
 #include "hw/hw.h"
@@ -3303,7 +3304,7 @@ static QDict *monitor_parse_arguments(Monitor *mon,
                         monitor_printf(mon, "enter a positive value\n");
                         goto fail;
                     }
-                    val <<= 20;
+                    val *= MiB;
                 }
                 qdict_put_int(qdict, key, val);
             }