[llvm] [LLVM][Docs][SPIRV] Correct `-spirv-ext` option name, reorder (PR #150423)

[Nathan Gauër via llvm-commits]

================
@@ -131,9 +131,20 @@ Extensions
 
 The SPIR-V backend supports a variety of `extensions <https://github.com/KhronosGroup/SPIRV-Registry/tree/main/extensions>`_
 that enable or enhance features beyond the core SPIR-V specification.
-These extensions can be enabled using the ``-spirv-extensions`` option
-followed by the name of the extension(s) you wish to enable. Below is a
-list of supported SPIR-V extensions, sorted alphabetically by their extension names:
+The enabled extensions can be controlled using the ``-spirv-ext`` option followed by a list of
+extensions to enable or disable, each prefixed with ``+`` or ``-``, respectively.
+
+To enable multiple extensions, list them separated by comma. For example, to enable support for atomic operations on floating-point numbers and arbitrary precision integers, use:
+
+``-spirv-ext=+SPV_EXT_shader_atomic_float_add,+SPV_INTEL_arbitrary_precision_integers``
+
+To enable all extensions, use the following option:
+``-spirv-ext=all``
----------------
Keenuts wrote:

```suggestion
To enable all extensions, use the following option:
``-spirv-ext=all``
To enable all KHR extensions, use the following option:
``-spirv-ext=khr``
```

https://github.com/llvm/llvm-project/pull/150423