pc: Eliminate pc_common_machine_options()

All TYPE_PC_MACHINE subclasses call pc_common_machine_options().
TYPE_PC_MACHINE can simply initialize the common options on class_init
directly.

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
