cpu: Introduce CPU model deprecation API

Implement the ability of marking some versions deprecated. When
that CPU model is chosen, print a warning.  The warning message
can be customized, e.g. suggesting an alternative CPU model to be
used instead.

The deprecation message will be printed by x86_cpu_list_entry(),
e.g. '-cpu help'.

QMP command 'query-cpu-definitions' will return a bool value
indicating the deprecation status.

Signed-off-by: Robert Hoo <robert.hu@linux.intel.com>
Message-Id: <1600758855-80046-1-git-send-email-robert.hu@linux.intel.com>
[ehabkost: reword commit message]
[ehabkost: Handle NULL cpu_type]
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
diff --git a/qapi/machine-target.json b/qapi/machine-target.json
index 698850c..fec3bb8 100644
--- a/qapi/machine-target.json
+++ b/qapi/machine-target.json
@@ -286,6 +286,10 @@
 #            in the VM configuration, because aliases may stop being
 #            migration-safe in the future (since 4.1)
 #
+# @deprecated: If true, this CPU model is deprecated and may be removed in
+#              in some future version of QEMU according to the QEMU deprecation
+#              policy. (since 5.2)
+#
 # @unavailable-features is a list of QOM property names that
 # represent CPU model attributes that prevent the CPU from running.
 # If the QOM property is read-only, that means there's no known
@@ -310,7 +314,8 @@
             'static': 'bool',
             '*unavailable-features': [ 'str' ],
             'typename': 'str',
-            '*alias-of' : 'str' },
+            '*alias-of' : 'str',
+            'deprecated' : 'bool' },
   'if': 'defined(TARGET_PPC) || defined(TARGET_ARM) || defined(TARGET_I386) || defined(TARGET_S390X) || defined(TARGET_MIPS)' }
 
 ##