perf hist: Factor out __hpp__fmt_print()

Split the logic to print the histogram values according to the format
string.  This was used in 3 different places so it's better to move out
the logic into a function.

Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Link: https://lore.kernel.org/r/20240607202918.2357459-2-namhyung@kernel.org