Help: Update CUDA_ARCHITECTURES docs for generic all/all-major support

Since commit 8f64df0a7c (CUDA: Generic all and all-major support,
2021-12-19, v3.23.0-rc1~23^2), these special values do not require any
specific compiler or version.

While at it, re-organize CUDA_ARCHITECTURES special value documentation.
Move the `versionadded` markup inside each special value so we can add
more in future versions.

Help/prop_tgt/CUDA_ARCHITECTURES.rst

@@ -20,17 +20,19 @@ variable if it is set when a target is created.
 The ``CUDA_ARCHITECTURES`` target property must be set to a non-empty value on targets
 that compile CUDA sources, or it is an error.  See policy :policy:`CMP0104`.
 
-.. versionadded:: 3.23
+The ``CUDA_ARCHITECTURES`` may be set to one of the following special values:
 
-  The ``CUDA_ARCHITECTURES`` may be set to the following special keywords:
+``all``
+  .. versionadded:: 3.23
 
-  ``all``
-    Requires NVIDIA 11.5+. Will compile for all supported major and minor real
-    architectures, and the highest major virtual architecture.
+  Compile for all supported major and minor real architectures,
+  and the highest major virtual architecture.
 
-  ``all-major``
-    Requires NVIDIA 11.5+. Will compile for all supported major real
-    architectures, and the highest major virtual architecture.
+``all-major``
+  .. versionadded:: 3.23
+
+  Compile for all supported major real architectures, and the highest
+  major virtual architecture.
 
 Examples
 ^^^^^^^^