qapi: generate trace events by default

We don't generate trace events for tests/ and qga/ because that it is
not simple and not necessary. We have corresponding comments in both
tests/meson.build and qga/meson.build.

Still to not miss possible future qapi code generation call, and not to
forget to enable trace events generation, let's enable it by default.
So, turn option --gen-trace into opposite --no-trace-events and use new
option only in tests/ and qga/ where we already have good comments why
we don't generate trace events code.

Note that this commit enables trace-events generation for qapi-gen.py
call from tests/qapi-schema/meson.build and storage-daemon/meson.build.
Still, both are kind of noop: tests/qapi-schema/ doesn't seem to
generate any QMP command code and no .trace-events files anyway,
storage-daemon/ uses common QMP command implementations and just
generate empty .trace-events

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-Id: <20220126161130.3240892-8-vsementsov@virtuozzo.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>

tests/meson.build

@@ -44,7 +44,8 @@ test_qapi_files = custom_target('Test QAPI files',
                                              'qapi-schema/include/sub-module.json',
                                              'qapi-schema/sub-sub-module.json'),
                                 command: [ qapi_gen, '-o', meson.current_build_dir(),
-                                           '-b', '-p', 'test-', '@INPUT0@' ],
+                                           '-b', '-p', 'test-', '@INPUT0@',
+                                           '--suppress-tracing' ],
                                 depend_files: qapi_gen_depends)
 
 # meson doesn't like generated output in other directories