Adding a 64x64 transform mode

Preliminary 64x64 transform implementation.
Includes all code changes.
All mismatches resolved.

Coding results for derf and stdhd are within noise. stdhd is slightly
higher, derf is slightly lower.

To be further refined.

Change-Id: I091c183f62b156d23ed6f648202eb96c82e69b4b
Merge "Adding a 64x64 transform mode" into nextgen