qapi: Plug trivial documentation holes around former simple unions

The conversion of simple to flat unions left the @data members
undocumented.  Add documentation where it's trivial.  Copy verbatim
from the wrapped type's description where possible.

Leftovers: String (to be taken care of in the next commit), and
TransActionAction (left for another day).

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-ID: <20240205074709.3613229-13-armbru@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>

qapi/machine.json

@@ -1396,6 +1396,8 @@
 ##
 # @PCDIMMDeviceInfoWrapper:
 #
+# @data: PCDIMMDevice state information
+#
 # Since: 2.1
 ##
 { 'struct': 'PCDIMMDeviceInfoWrapper',
@@ -1404,6 +1406,8 @@
 ##
 # @VirtioPMEMDeviceInfoWrapper:
 #
+# @data: VirtioPMEM state information
+#
 # Since: 2.1
 ##
 { 'struct': 'VirtioPMEMDeviceInfoWrapper',
@@ -1412,6 +1416,8 @@
 ##
 # @VirtioMEMDeviceInfoWrapper:
 #
+# @data: VirtioMEMDevice state information
+#
 # Since: 2.1
 ##
 { 'struct': 'VirtioMEMDeviceInfoWrapper',
@@ -1420,6 +1426,8 @@
 ##
 # @SgxEPCDeviceInfoWrapper:
 #
+# @data: Sgx EPC state information
+#
 # Since: 6.2
 ##
 { 'struct': 'SgxEPCDeviceInfoWrapper',
@@ -1428,6 +1436,8 @@
 ##
 # @HvBalloonDeviceInfoWrapper:
 #
+# @data: hv-balloon provided memory state information
+#
 # Since: 8.2
 ##
 { 'struct': 'HvBalloonDeviceInfoWrapper',