_platform/platform.py: Add alias for sun4v

Chandan Singhrequested to merge
chandan/platform-sunos into master

Some Solaris 11 servers report uname -m as sun4v. It uses the same SPARC v9 processor architecture so add an alias for it as we already support sparc-v9.

uname -a output for reference:

    $ uname -a
    SunOS sundev1 5.11 11.3 sun4v sparc sun4v Solaris

Merge request reports