posix: sys/stat.h: move declarations to posix_types.h

A number of types such as uid_t, gitd_t, etc, were defined in
sys/stat.h to workaround compatibility issues many years ago.

Since posix_types.h is slated to become equivalent to
sys/types.h in terms of standard headers, move these types
to where they belong.

For more information, please see

https://pubs.opengroup.org/onlinepubs/9699919799/\


 basedefs/sys_types.h.html

Signed-off-by: Chris Friedt <cfriedt@tenstorrent.com>
(cherry picked from commit 6667b500)