vl: 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: <20180625124238.25339-44-f4bug@amsat.org>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

vl.c

@@ -23,6 +23,7 @@
  */
 
 #include "qemu/osdep.h"
+#include "qemu/units.h"
 #include "qapi/error.h"
 #include "qemu-version.h"
 #include "qemu/cutils.h"
@@ -2808,8 +2809,8 @@ static void set_memory_options(uint64_t *ram_slots, ram_addr_t *maxram_size,
         if (g_ascii_isdigit(mem_str[strlen(mem_str) - 1])) {
             uint64_t overflow_check = sz;
 
-            sz <<= 20;
-            if ((sz >> 20) != overflow_check) {
+            sz *= MiB;
+            if (sz / MiB != overflow_check) {
                 error_report("too large 'size' option value");
                 exit(EXIT_FAILURE);
             }