Move NBI put-with-signal apiimpnotes to apinotes

Previously, we had the information about the signal updates atomicity
guarantees in the notes to implementors section for put-with-signal.
We are not now moving this into main notes section. We have also
clarified the atomicity guarantees by refering to atomicty section.

content/shmem_put_signal.tex

@@ -75,13 +75,12 @@
     routine and another data transfer. For example, the delivery of the signal
     word in a sequence consisting of a put routine followed by a put-with-signal
     routine does not imply delivery of the put routine's data.
-}
 
-\apiimpnotes{
-    Implementations must ensure that put-with-signal routines are compatible
-    with all point-to-point synchronization interfaces. The delivery of
-    \signal{} flag on the remote \ac{PE} must not cause partial updates. This
-    requires the update on \signal{} flag to be an atomic memory operation.
+    The put-with-signal routines are compatible with all point-to-point
+    synchronization interfaces. The delivery of \VAR{signal} flag on the remote
+    \ac{PE} must not cause partial updates. This requires the update on
+    \VAR{signal} flag to be an atomic operation, with atomicity guarantees
+    described in Section~\ref{subsec:amo_guarantees}.
 }
 
 \begin{apiexamples}