Reduce IndirectReferenceTable memory usage

Changed the slot side table and the main table to be a single
table, reduced number of slots per reference from 4 to 3 to make
the IrtEntry a power of 2 size.

Before:
20848 kB: Dalvik Other

After:
16760 kB: Dalvik Other

Bug: 17643507

(cherry picked from commit a1de6b93)

Change-Id: I362475235a887c60eff6870bb10051a6be3d5814