arm64: microbench: its: Add LPI latency test

Triggers LPIs through the INT command and test the latency.
Mostly inherited form commit 0ef02cd6(arm/arm64: ITS: INT
functional tests).

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