isa: configure serial+parallel by index.

isa: configure serial+parallel by index.

This patch adds a 'index' property to the isa-parallel and isa-serial
devices.  This can be used to create devices with the default isa irqs
and ioports by simply specifying the index, i.e.

   -device isa-serial,index=1

instead of

   -device isa-serial,iobase=0x2f8,irq=3

for ttyS1 aka com2.  Likewise for parallel ports.

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