Only use av1_inv_txfm2d_add_32x32_avx2 for DCT_DCT
Only use av1_inv_txfm2d_add_32x32_avx2 for DCT_DCT

The AVX2 code only supports DCT_DCT. For other transform types, use
the C fallback.

Change-Id: I6b472ebd7d963c02aae80ff5846b7f2dcaf092ea

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