hw/pci-host/versatile.c: Provide property for forcing broken IRQ mapping

hw/pci-host/versatile.c: Provide property for forcing broken IRQ mapping

Although we try our best to automatically detect broken versions
of Linux which assume the old broken IRQ mapping we used to implement
for our model of the Versatile PCI controller, it turns out that
some particularly new kernels manage to outwit the autodetection.

We therefore provide a property for enabling the old broken IRQ
mapping, so that if users happen to have such a kernel they can
work around its deficiencies with the command line option:
  -global versatile_pci.broken-irq-mapping=1

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 1368545616-22344-4-git-send-email-peter.maydell@linaro.org
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>