[OpenMP] Add docs for fb_nullify/fb_preserve (llvm#169558)

Adding documentation following the merge of
llvm#168905.

Author: zahiraam

clang/docs/OpenMPSupport.rst

@@ -580,6 +580,8 @@ implementation.
 | need_device_addr modifier for adjust_args clause            | :part:`partial`           | :none:`unclaimed`         | Parsing/Sema: https://github.com/llvm/llvm-project/pull/143442           |
 |                                                             |                           |                           |               https://github.com/llvm/llvm-project/pull/149586           |
 +-------------------------------------------------------------+---------------------------+---------------------------+--------------------------------------------------------------------------+
+| need_device_ptr modifier for adjust_args clause             | :part:`unclaimed`         | :none:`unclaimed`         |                                                                          |
++-------------------------------------------------------------+---------------------------+---------------------------+--------------------------------------------------------------------------+
 | Prescriptive num_threads                                    | :good:`done`              | :none:`unclaimed`         |  https://github.com/llvm/llvm-project/pull/160659                        |
 |                                                             |                           |                           |  https://github.com/llvm/llvm-project/pull/146403                        |
 |                                                             |                           |                           |  https://github.com/llvm/llvm-project/pull/146404                        |
@@ -631,7 +633,9 @@ implementation.
 |                                                             |                           |                           | RT: @abhinavgaba (https://github.com/llvm/llvm-project/pull/149036,      |
 |                                                             |                           |                           | https://github.com/llvm/llvm-project/pull/158370)                        |
 +-------------------------------------------------------------+---------------------------+---------------------------+--------------------------------------------------------------------------+
-
+| need_device_ptr modifier for adjust_args clause             | :part:`partial`           | :none:`unclaimed`         | Clang Parsing/Sema: https://github.com/llvm/llvm-project/pull/168905     |
+|                                                             |                           |                           | https://github.com/llvm/llvm-project/pull/169558                         |
++-------------------------------------------------------------+---------------------------+---------------------------+--------------------------------------------------------------------------+
 
 OpenMP Extensions
 =================

clang/docs/ReleaseNotes.rst

@@ -763,6 +763,9 @@ OpenMP Support
 - Updated parsing and semantic analysis support for ``nowait`` clause to accept
   optional argument in OpenMP >= 60.
 - Added support for ``default`` clause on ``target`` directive.
+- Added parsing and semantic analysis support for ``need_device_ptr`` modifier
+  to accept an optional fallback argument (``fb_nullify`` or ``fb_preserve``)
+  with OpenMP >= 61.
 
 Improvements
 ^^^^^^^^^^^^