[llvm] [Doc][AMDGPU] Document the waitcnts required before SCOPE_SYS stores on GFX12 (PR #156424)

[Tony Tye via llvm-commits]

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@@ -14669,7 +14677,20 @@ the instruction in the code sequence that references the table.
                                - wavefront    - generic
                                - workgroup                 - Apply :ref:`amdgpu-amdhsa-memory-model-code-sequences-gfx12-scopes-table`.
                                - agent
-                               - system
+     store atomic monotonic    - system       - global   1. | ``s_wait_loadcnt 0x0``
+                                              - generic     | ``s_wait_storecnt 0x0``
+                                                            | ``s_wait_kmcnt 0x0``
+                                                            | ``s_wait_samplecnt 0x0``
+                                                            | ``s_wait_bvhcnt 0x0``
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t-tye wrote:

So ``s_wait_dscnt 0x0`` is not needed? I notice it is present for the store release.

https://github.com/llvm/llvm-project/pull/156424