selftests/resctrl: Share show_cache_info() by CAT and CMT tests

show_cache_info() functions are defined separately in CAT and CMT
tests. But the functions are same for the tests and unnecessary
to be defined separately. Share the function by the tests.

Suggested-by: Shuah Khan <skhan@linuxfoundation.org>
Tested-by: Babu Moger <babu.moger@amd.com>
Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>