Change the CONFIGs for PCI EXPRESS and make module name more
clear for code files.

Signed-off-by: Yang Zhong <yang.zhong@intel.com>
Cc: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20190202072456.6468-5-yang.zhong@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>