Some machines use floppy controllers via the SysBus interface,
and don't need to pull in all the SysBus code.
Extract the SysBus specific code to a new unit: fdc-sysbus.c,
and add a new Kconfig symbol: "FDC_SYSBUS".

Reviewed-by: John Snow <jsnow@redhat.com>
Acked-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Reviewed-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-id: 20210614193220.2007159-6-philmd@redhat.com
Signed-off-by: John Snow <jsnow@redhat.com>