simpleperf: add --cpu to filter cpus in report command.

Also refactor report command to use PreprocessOptions().
Also refactor GetCpusFromString() to check input errors from the --cpu
option.
Also simplify return type of OptionValueMap::PullValues(), to reduce one
block layer when using it.

Bug: 160611908
Test: run simpleperf_unit_test.

Change-Id: Ic6749909c73f448dd073ef5501834ef0afc341cb
12 files changed