qemu: replace calls to virDomainPCIAddressReserveNext*() with static function
    
    An upcoming commit will remove the "flag" argument from all the calls
    to reserve the next available address|slot, but I don't want to change
    the arguments in the hypervisor-agnostic
    virDomainPCIAddressReserveNext*() functions, so this patch places a
    simple qemu-specific wrapper around those functions - the new
    functions don't take a flags arg, but grab it from the device's
    info->pciConnectFlags.