linux-user/aarch64: Choose SYNC as the preferred MTE mode

linux-user/aarch64: Choose SYNC as the preferred MTE mode

The API does not generate an error for setting ASYNC | SYNC; that merely
constrains the selection vs the per-cpu default.  For qemu linux-user,
choose SYNC as the default.

Cc: qemu-stable@nongnu.org
Reported-by: Gustavo Romero <gustavo.romero@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Tested-by: Gustavo Romero <gustavo.romero@linaro.org>
Message-id: 20240207025210.8837-2-richard.henderson@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>