arm64: add micro-bench

Here we provide the support for measuring various micro level
operations on arm64. Measurements are currently obtained using
timer counters. Further modifications in KVM will be required
to support timestamping using cycle counters, as KVM now disables
accesses to the PMU counters from the VM.

Signed-off-by: Shih-Wei Li <shihwei@cs.columbia.edu>
Signed-off-by: Christoffer Dall <cdall@cs.columbia.edu>
Signed-off-by: Andrew Jones <drjones@redhat.com>
Acked-by: Christoffer Dall <christoffer.dall@arm.com>
Tested-by: Christoffer Dall <christoffer.dall@arm.com>
Tested-by: Shih-Wei Li <shihwei@cs.columbia.edu>