perf c2c: Use more explicit headers for HITM

Local and remote HITM use the headers 'Lcl' and 'Rmt' respectively,
suppose if we want to extend the tool to display these two dimensions
under any one metrics, users cannot understand the semantics if only
based on the header string 'Lcl' or 'Rmt'.

To explicit express the meaning for HITM items, this patch changes the
headers string as "LclHitm" and "RmtHitm", the strings are more readable
and this allows to extend metrics for using HITM items.

Signed-off-by: Leo Yan <leo.yan@linaro.org>
Tested-by: Joe Mario <jmario@redhat.com>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Link: https://lore.kernel.org/r/20201014050921.5591-6-leo.yan@linaro.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>