ls(1): Update POSIX conformance from 2001 to 2008

• Update the options that are non-existing in POSIX from 2001 to 2008
• Update POSIX conformance in the STANDARDS section from 2001 to 2008

Verified by checking [1].

[1] https://pubs.opengroup.org/onlinepubs/9699919799.2016edition/toc.htm

PR: 140435
Submitted by: Dan Lukes <dan at obluda dot cz>
Reviewed by: bcr
Approved by: bcr
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D26096