perf tools: Create function to parse time percent

Current perf report/script/... have a --time option to limit the time
range of output. But right now it only supports absolute time, add
support for time percentage.

For example:

1. Select the second 10% time slice
   perf report --time 10%/2

2. Select from 0% to 10% time slice
   perf report --time 0%-10%

It also support the multiple time ranges.

3. Select the first and second 10% time slices
   perf report --time 10%/1,10%/2

4. Select from 0% to 10% and 30% to 40% slices
   perf report --time 0%-10%,30%-40%

Changelog:

v4: An issue is found. Following passes.
    perf script --time 10%/10x12321xsdfdasfdsafdsafdsa

    Now it uses strtol to replace atoi.

Committer notes:

This just puts in place the infrastructure, so the examples in this cset
comment will only work later, after more patches in this series are
applied.

Signed-off-by: Jin Yao <[email protected]>
Acked-by: Jiri Olsa <[email protected]>
Cc: Alexander Shishkin <[email protected]>
Cc: Andi Kleen <[email protected]>
Cc: Kan Liang <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>

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