doc: posix: options: make column size consistent

For some reason, when the "Supported" coumn of the posix option
documentation included large strings, it would distort the size
of the entire table.

Move blurbs about undefined behaviour and failing with ENOSYS
to a paragraph above the table, so that all tables have a
homogeneous size.

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

Author: cfriedt

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

@@ -367,7 +367,7 @@ to ``ENOSYS`` :ref:`†<posix_undefined_behaviour>`.
     setsockopt(),yes
     shutdown(),yes
     socket(),yes
-    sockatmark(),yes (will fail with ``ENOSYS``:ref:`†<posix_undefined_behaviour>`)
+    sockatmark(),yes :ref:`†<posix_undefined_behaviour>`
     socketpair(),yes
 
 .. _posix_option_group_pipe:
@@ -743,6 +743,10 @@ _POSIX_MONOTONIC_CLOCK
 _POSIX_PRIORITY_SCHEDULING
 ++++++++++++++++++++++++++
 
+As processes are not yet supported in Zephyr, the functions ``sched_rr_get_interval()``,
+``sched_setparam()``, and ``sched_setscheduler()`` are expected to fail setting ``errno``
+to ``ENOSYS``:ref:`†<posix_undefined_behaviour>`.
+
 .. csv-table:: _POSIX_PRIORITY_SCHEDULING
    :header: API, Supported
    :widths: 50,10
@@ -751,9 +755,9 @@ _POSIX_PRIORITY_SCHEDULING
     sched_get_priority_min(),yes
     sched_getparam(),yes
     sched_getscheduler(),yes
-    sched_rr_get_interval(),yes (will fail with ``ENOSYS``:ref:`†<posix_undefined_behaviour>`)
-    sched_setparam(),yes (will fail with ``ENOSYS``:ref:`†<posix_undefined_behaviour>`)
-    sched_setscheduler(),yes (will fail with ``ENOSYS``:ref:`†<posix_undefined_behaviour>`)
+    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: