arm64: microbench: Generalize ipi test names

Later patches will use these functions for gic(ipi/lpi/timer) 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>