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: Mark McLoughlin <markmc@redhat.com>
Signed-off-by: Anthony 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;