The patch adds the flexibility to use standard EOB based coding
on smaller block sizes and nzc based coding on larger blocksizes.
The tx-sizes that use nzc based coding and those that use EOB based
coding are controlled by a function get_nzc_used().
By default, this function uses nzc based coding for 16x16 and 32x32
transform blocks, which seem to bridge the performance gap
substantially.

All sets are now lower by 0.5% to 0.7%, as opposed to ~1.8% before.

Change-Id: I06abed3df57b52d241ea1f51b0d571c71e38fd0b