Add isa_reserve_irq().

Add isa_reserve_irq().

Introduce isa_reserve_irq() which marks an irq reserved and returns
the appropriate qemu_irq entry from the i8259 table.

isa_reserve_irq() is a temporary interface to be used to allocate ISA
IRQs for devices which have not yet been converted to qdev, and for
special cases which are not suited for qdev conversions, such as the
'ferr'.

This patch goes on top of Gerd Hoffmann's which makes isa-bus.c own
the ISA irq table.

[ added isa-bus.o to some targets to fix build failures  -- kraxel ]

Signed-off-by: Jes Sorensen <[email protected]>
Signed-off-by: Gerd Hoffmann <[email protected]>
Signed-off-by: Anthony Liguori <[email protected]>