Add machine type aliases

Add an 'alias' field to QEMUMachine and display it in the output of
'qemu -M ?' with an '(aliased to foo)' suffix.

Aliases can change targets in newer versions of qemu, so management tools
may choose canonicalize machine types to ensure that if a user chooses an
alias, that the actual machine type used will remain compatible in
future.

This is intended to mimic a symlink to a machine description file.
Signed-off-by: NMark McLoughlin <markmc@redhat.com>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

hw/boards.h

@@ -14,6 +14,7 @@ typedef void QEMUMachineInitFunc(ram_addr_t ram_size,
 
 typedef struct QEMUMachine {
     const char *name;
+    const char *alias;
     const char *desc;
     QEMUMachineInitFunc *init;
     int use_scsi;

vl.c

@@ -3359,6 +3359,8 @@ static QEMUMachine *find_machine(const char *name)
     for(m = first_machine; m != NULL; m = m->next) {
         if (!strcmp(m->name, name))
             return m;
+        if (m->alias && !strcmp(m->alias, name))
+            return m;
     }
     return NULL;
 }
@@ -4995,6 +4997,9 @@ int main(int argc, char **argv, char **envp)
                     QEMUMachine *m;
                     printf("Supported machines are:\n");
                     for(m = first_machine; m != NULL; m = m->next) {
+                        if (m->alias)
+                            printf("%-10s %s (alias of %s)\n",
+                                   m->alias, m->desc, m->name);
                         printf("%-10s %s%s\n",
                                m->name, m->desc,
                                m->is_default ? " (default)" : "");