Refactor dump_memory function.

- Add dumping memory around registers for x86/x86_64.
- Add unit tests for new dump_memory function.
- Cleanup all of the machine.cpp files.
- Increase the high address check for 32 bit, and decrease the high
  address allowed for 64 bit slightly to match mips64.

Bug: 21206576
(cherry picked from commit e8bc77eb)

Change-Id: I49ec237e30076a232f084da1072bf9aba15dc0cd