Change txfm_type decision

Change txfm_type decision

The changing in intra coding to base on transform block, i.e. pred->
txfm->quant->dequant-itxfm->recon, made all blocks within a prediction
unit behave consistently, there is no longer a need to handle blocks
differently based on the position within a predicitn block. So this
commit simplifies the decision of transform type to be based on
prediction mode only.

Change-Id: If96cb72386f2e9186126ace88afa35ef085b6c96