Turn off 32x32 transform type selection

Temporarily disable transform type selection for 32x32 transform
block size. This speeds up the encoding process. For bus at CIF
150 frames, the encoding time goes from 896s -> 762s (11% faster).
The compression performance for lowres set is improved by 0.15%,
and -0.029% for hdres.

Change-Id: If239b272970eb302150bec13b8cf192fbe045332