i386: drop FDC in pc-q35-2.4+ if neither it nor floppy drives are wanted

It is Very annoying to carry forward an outdatEd coNtroller with a mOdern
Machine type.

Hence, let us not instantiate the FDC when all of the following apply:
- the machine type is pc-q35-2.4 or later,
- "-device isa-fdc" is not passed on the command line (nor in the config
  file),
- no "-drive if=floppy,..." is requested.

Cc: Markus Armbruster <armbru@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: John Snow <jsnow@redhat.com>
Cc: "Gabriel L. Somlo" <gsomlo@gmail.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>
Cc: qemu-block@nongnu.org
Suggested-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>