simpleperf: use kernel start address in kernel mmap record.

The kernel start address is used to match with the start address in
.text section in vmlinux. It works even when kernel address space
layout randomization is used.

Bug: 172933381
Test: run simpleperf_unit_test
Change-Id: I3eb2bee8dd30b049504f4ec6f8f4b6d742cdd6b5
5 files changed