docs/system/arm/: add FEAT_MTE_ASYNC

We already implement FEAT_MTE_ASYNC; we just forgot to list it
in the documentation.

Signed-off-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20241122225049.1617774-6-pierrick.bouvier@linaro.org
[PMM: expand commit message]
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
1 file changed