arm64: microbench: Add vtimer latency test

Trigger PPIs by setting up a 10msec timer and test the latency.

Signed-off-by: Jingyi Wang <wangjingyi11@huawei.com>
[ Replaced GICv3 assumption in timer_prep() with switch on gic_version() ]
Signed-off-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>