arm64: microbench: Allow each test to specify its running times

For some test in micro-bench can be time consuming, we add a
micro-bench test parameter to allow each individual test to specify
its running times.

Signed-off-by: Jingyi Wang <wangjingyi11@huawei.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Signed-off-by: Andrew Jones <drjones@redhat.com>