simpleperf: add class interface to read elf files.

This is to keep file mapping memory buffer. And support reading
more than one content in one open instance in the future.
It also supports embedded elf files in apks as normal elf files.

Bug: 151665001
Test: run simpleperf_unit_test.
Change-Id: Ia424926d112cbcd9970f11ffa56d047ff6df7872
5 files changed