Google does not assess the backlinks you provide for the sitemaps. It would not be useful gesture anyway.
It is better to build sitemap.php (or html) page, to which you link from your homepage. It has the same links as xml but is included in the site structure.
Reason! ??? SEO is done for a PURPOSE, right? Can I ask you what PURPOSE will it serve if you waste back links to your XML sitemap? You want SEARCHERS to land on it and "trash it" in milliseconds or microseconds? And FYI Google does not index XML. Official source here Cheers
Don't build backlinks for your xml sitemap, it's not reuqired. If you have a link to your xml sitemap within your pages, put rel="nofollow".