qapi: Move RTC_CHANGE back out of target schema

qapi: Move RTC_CHANGE back out of target schema

This commit effectively reverts commit 183e4281a30962, which moved
the RTC_CHANGE event to the target schema.  That change was an
attempt to make the event target-specific to improve introspection,
but the event isn't really target-specific: it's machine or device
specific.  Putting RTC_CHANGE in the target schema with an ifdef list
reduces maintainability (by adding an if: list with a long list of
targets that needs to be manually updated as architectures are added
or removed or as new devices gain the RTC_CHANGE functionality) and
increases compile time (by preventing RTC devices which emit the
event from being "compile once" rather than "compile once per
target", because qapi-events-misc-target.h uses TARGET_* ifdefs,
which are poisoned in "compile once" files.)

Move RTC_CHANGE back to misc.json.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Acked-by: Greg Kurz <groug@kaod.org>
Message-Id: <20220221192123.749970-2-peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Markus Armbruster <armbru@redhat.com>