hw/pci: define msi_nonbroken in pci-stub

hw/pci: define msi_nonbroken in pci-stub

The kludged field 'msi_nonbroken' is declared in "hw/pci/msi.h" and defined in
hw/pci/msi.c.
When using an ARM config with CONFIG_PCI disabled, hw/pci/msi.c is not included.
Without being PCI-related, the files hw/intc/arm_gicv[23*].c do access this
field (to enable the kludge if PCI is enabled).
The final link fails since hw/pci/msi.c is not included.
Defining this field in pci-stub is safe enough for configs without CONFIG_PCI.

Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>