tests/qtest/arm-cpu-features: Add feature setting tests

tests/qtest/arm-cpu-features: Add feature setting tests

Some cpu features may be enabled and disabled for all configurations
that support the feature. Let's test that.

A recent regression[*] inspired adding these tests.

[*] '-cpu host,pmu=on' caused a segfault

Signed-off-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-id: 20200623090622.30365-2-philmd@redhat.com
Message-Id: <20200623082310.17577-1-drjones@redhat.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>