mc146818rtc: move structure to header file

mc146818rtc: move structure to header file

We are now able to embed a timer in another object.

Acked-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Hervé Poussineau <hpoussin@reactos.org>
Message-Id: <20171216090228.28505-4-hpoussin@reactos.org>
Reviewed-by: Aleksandar Markovic <amarkovic@wavecomp.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20191018133547.10936-2-philmd@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>