qapi/machine: Make @dump-skeys command generic

Reduce misc-target.json by one target specific command.

Error message is returned for machines not implementing
TYPE_DUMP_SKEYS_INTERFACE:

  $ qemu-system-aarch64 -M virt -S -qmp stdio
  {"QMP": {"version": {"qemu": {"micro": 50, "major": 9}}, "capabilities": ["oob"]}}
  { "execute": "qmp_capabilities" }
  {"return": {}}
  { "execute": "dump-skeys", "arguments": { "filename": "/tmp/foo" }  }
  {"error": {"class": "GenericError", "desc": "Storage keys information not available for this architecture"}}

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-ID: <20250310151414.11550-5-philmd@linaro.org>
Signed-off-by: Thomas Huth <thuth@redhat.com>

qapi/machine.json

@@ -1898,3 +1898,21 @@
 { 'command': 'x-query-interrupt-controllers',
   'returns': 'HumanReadableText',
   'features': [ 'unstable' ]}
+
+##
+# @dump-skeys:
+#
+# Dump the storage keys for an s390x guest
+#
+# @filename: the path to the file to dump to
+#
+# Since: 2.5
+#
+# .. qmp-example::
+#
+#     -> { "execute": "dump-skeys",
+#          "arguments": { "filename": "/tmp/skeys" } }
+#     <- { "return": {} }
+##
+{ 'command': 'dump-skeys',
+  'data': { 'filename': 'str' } }

qapi/misc-target.json

@@ -274,25 +274,6 @@
   'returns': 'SevAttestationReport',
   'if': 'TARGET_I386' }
 
-##
-# @dump-skeys:
-#
-# Dump guest's storage keys
-#
-# @filename: the path to the file to dump to
-#
-# Since: 2.5
-#
-# .. qmp-example::
-#
-#     -> { "execute": "dump-skeys",
-#          "arguments": { "filename": "/tmp/skeys" } }
-#     <- { "return": {} }
-##
-{ 'command': 'dump-skeys',
-  'data': { 'filename': 'str' },
-  'if': 'TARGET_S390X' }
-
 ##
 # @GICCapability:
 #