posix: add Kconfig.deprecated

There will be some POSIX Kconfig symbols that will be deprecated
in favour of Kconfig symbols that are exact matches for those in
the POSIX specification (1003.1-2017).

Create the empty Kconfig file now, and then incrementally add to
it as non-standard POSIX Kconfig options are replaced with
standard-like POSIX Kconfig options.

Signed-off-by: Chris Friedt <cfriedt@tenstorrent.com>