s390x/pci: use a reserved ID for the default PCI group

s390x/pci: use a reserved ID for the default PCI group

The current default PCI group being used can technically collide with a
real group ID passed from a hostdev.  Let's instead use a group ID that
comes from a special pool (0xF0-0xFF) that is architected to be reserved
for simulated devices.

Fixes: 28dc86a072 ("s390x/pci: use a PCI Group structure")
Signed-off-by: Matthew Rosato <mjrosato@linux.ibm.com>
Reviewed-by: Eric Farman <farman@linux.ibm.com>
Reviewed-by: Pierre Morel <pmorel@linux.ibm.com>
Message-Id: <20211203142706.427279-2-mjrosato@linux.ibm.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>