av1_inv_txfm_test: fix decode-only build
av1_inv_txfm_test: fix decode-only build

fdct's are only enabled with --enable-av1-encoder

Change-Id: Iaf1dfdf713f2ecd1d215ba7ec635f353c02fa4d0

luctrudeau/aom,luctrudeau/aom,shacklettbp/aom,luctrudeau/aom,shacklettbp/aom,mbebenita/aom,mbebenita/aom,GrokImageCompression/aom,mbebenita/aom,smarter/aom,GrokImageCompression/aom,mbebenita/aom,luctrudeau/aom,mbebenita/aom,smarter/aom,GrokImageCompression/aom,mbebenita/aom,shacklettbp/aom,shacklettbp/aom,smarter/aom,GrokImageCompression/aom,GrokImageCompression/aom,luctrudeau/aom,smarter/aom,smarter/aom,smarter/aom,mbebenita/aom,shacklettbp/aom,GrokImageCompression/aom,mbebenita/aom,shacklettbp/aom,luctrudeau/aom,mbebenita/aom