Implement boot image extension relocation.

The creation of boot image extensions and other aspects
of loading them shall be implemented in separate CLs.

Test: m test-art-host-gtest
Test: testrunner.py --host --optimizing
Test: aosp_taimen-userdebug boots.
Change-Id: I1630d6cc44550bc0db72cb5c4a8e08573cf3b92c
3 files changed