simpleperf: extract common code into report_utils.cpp

Extract common code in cmd_report_sample.cpp and
report_lib_interface.cpp, into report_utils.cpp.

Bug: 175163225
Test: run simpleperf_unit_test.
Test: run test.py TestReportLibs*.
Change-Id: Ic64956cd1a73ef3165337aa3509a15d14e095959
8 files changed