Install optional dependencies of QEMU to get better coverage.

Suggested-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20200322120104.21267-5-philmd@redhat.com>
Message-Id: <20200323161514.23952-11-alex.bennee@linaro.org>