doc: posix: move sched_yield() from to POSIX_THREADS_base

Move `sched_yield()` from the `_POSIX_PRIORITY_SCHEDULING` Option to the
`POSIX_THREADS_BASE` Option Group.

For more information, please see
https://pubs.opengroup.org/onlinepubs/9799919799/xrat/V4_subprofiles.html

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

Author: Chris Friedt

doc/services/portability/posix/option_groups/index.rst

@@ -650,6 +650,7 @@ Enable this option group with :kconfig:option:`CONFIG_POSIX_THREADS`.
     pthread_setspecific(),yes
     pthread_sigmask(),yes
     pthread_testcancel(),yes
+    sched_yield(),yes
 
 .. _posix_option_group_posix_threads_ext:
 
@@ -910,7 +911,6 @@ Enable this option with :kconfig:option:`CONFIG_POSIX_PRIORITY_SCHEDULING`.
     sched_rr_get_interval(),yes :ref:`†<posix_undefined_behaviour>`
     sched_setparam(),yes :ref:`†<posix_undefined_behaviour>`
     sched_setscheduler(),yes :ref:`†<posix_undefined_behaviour>`
-    sched_yield(),yes
 
 .. _posix_option_raw_sockets: