app/testpmd: print clock with CPU cycles per packet

app/testpmd: print clock with CPU cycles per packet

On aarch64 platforms, the cycles are counted using either a
low-resolution generic counter or a high-resolution PMU cycle counter.
Print the clock frequency along with CPU cycles/packet to identify which
cycle counter is being used.

Signed-off-by: Dharmik Thakkar <dharmik.thakkar@arm.com>
Reviewed-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
Reviewed-by: Phil Yang <phil.yang@arm.com>
Acked-by: Bernard Iremonger <bernard.iremonger@intel.com>