Switch to adding compat properties incrementaly instead of
completly overwriting compat_props per machine type.
That removes data duplication which we have due to nested
[PC|SPAPR]_COMPAT_* macros.

It also allows to set default device properties from
default foo_machine_options() hook, which will be used
in following patch for putting VMGENID device as
a function if ISA bridge on pc/q35 machines.
Suggested-by: NEduardo Habkost <ehabkost@redhat.com>
Signed-off-by: NIgor Mammedov <imammedo@redhat.com>
Acked-by: NCornelia Huck <cornelia.huck@de.ibm.com>
Reviewed-by: NEduardo Habkost <ehabkost@redhat.com>
[ehabkost: Fixed CCW_COMPAT_* and PC_COMPAT_0_* defines]
Signed-off-by: NEduardo Habkost <ehabkost@redhat.com>