qom: Make enum string tables const-correct

The enum string table parameters in various QOM/QAPI methods
are declared 'const char *strings[]'. This results in const
warnings if passed a variable that was declared as

   static const char * const strings[] = { .... };

Add the extra const annotation to the parameters, since
neither the string elements, nor the array itself should
ever be modified.

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>

scripts/qapi-types.py

@@ -105,7 +105,7 @@ struct %(name)s
 
 def generate_enum_lookup(name, values):
     ret = mcgen('''
-const char *%(name)s_lookup[] = {
+const char * const %(name)s_lookup[] = {
 ''',
                 name=c_name(name))
     i = 0
@@ -128,7 +128,7 @@ const char *%(name)s_lookup[] = {
 def generate_enum(name, values):
     name = c_name(name)
     lookup_decl = mcgen('''
-extern const char *%(name)s_lookup[];
+extern const char * const %(name)s_lookup[];
 ''',
                 name=name)