Rename isDexOptNeededInternal and add kSelfPatchOatNeeded

This change renames isDexOptNeededInternal to getDexOptNeeded and adds
another possible result: kSelfPatchOatNeeded. kSelfPatchOatNeeded is
returned when there is no odex file to relocate from but there is an
oat file that can be relocated in place.

Change-Id: Ib9a6373f98474f1242367b5285086251a9d580e5