Use av1_tx_type_cost() in choose_largest_tx_size()
Use av1_tx_type_cost() in choose_largest_tx_size()

BUG=aomedia:442

Change-Id: Ieef34848e73eb31428c6b8652312fc9421605033

GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom