rust: sort uml documentation arch support table

The arch_support table was not sorted alphabetically.
Sorts the table properly.

Fixes: 0438aadf ("rust: arch/um: Add support for CONFIG_RUST under x86_64 UML")
Link: https://lore.kernel.org/rust-for-linux/CANiq72nXMsnUsJNZOG-QZiCVOqa9dRUSMc4RAS3ExLZNJ7VhHg@mail.gmail.comReported-by: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
Signed-off-by: Thomas Bamelis <thomas@bamelis.dev>
Reviewed-by: David Gow <davidgow@google.com>
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Documentation/rust/arch-support.rst

@@ -15,7 +15,7 @@ support corresponds to ``S`` values in the ``MAINTAINERS`` file.
 ============  ================  ==============================================
 Architecture  Level of support  Constraints
 ============  ================  ==============================================
-``x86``       Maintained        ``x86_64`` only.
 ``um``        Maintained        ``x86_64`` only.
+``x86``       Maintained        ``x86_64`` only.
 ============  ================  ==============================================