simpleperf: fix potential unaligned memory access.

1. It is reported that when elf section headers are malformed,
GetBuildIdFromNoteSection() aborts with SIGBUS. So fix it to
accept not 4 bytes aligned section data.
2. Fix potential unaligned memory access in ConvertBytesToValue().

Test: run simpleperf_unit_test.
Change-Id: I2e1612a6567978e0b526b2274377765ba2837ec2
5 files changed