tests: timing_info: need to calibrate TSC frequency on x86

For x86, TSC is being used to gather timing information. However,
CONFIG_SYS_CLOCK_HW_CYCLES_PER_SEC is not the same as TSC
frequency when HPET (or other) timer is used. So use the system
clock to calibrate the TSC frequency so we can use it to
calculate timing information.

Signed-off-by: Daniel Leung <daniel.leung@intel.com>