isa bus irq changes and fixes.

isa bus irq changes and fixes.

Changes:

  (1) make isa-bus maintain isa irqs, complain when allocating
      already taken irqs.
  (2) note that (1) works only for isa devices converted to qdev
      already (floppy and ps2/kbd/mouse right now), so more work
      is needed to make this really useful.
  (3) split floppy init into isa and sysbus versions.
  (4) add sysbus->isa bridge & fix -M isapc breakage.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>